Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.34   11.217%   $230.5973   $230.60   $230.60   $230.60  
  Purchase #2 $216.71   13.286%   $245.5021   $245.50   $245.50   $245.50  
  Purchase #3 $150.61   13.495%   $170.9348   $170.93   $170.95   $170.90  
  Purchase #4 $232.41   6.691%   $247.9606   $247.96   $247.95   $248.00  
  Purchase #5 $247.82   13.151%   $280.4108   $280.41   $280.40   $280.40  
  Purchase #6 $186.87   8.781%   $203.2791   $203.28   $203.30   $203.30  
  Purchase #7 $94.84   13.534%   $107.6756   $107.68   $107.70   $107.70  
  7 purchase totals = $1,336.60       $1,486.3603   $1,486.36   $1,486.40   $1,486.40