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 $175.55   11.652%   $196.0051   $196.01   $196.00   $196.00  
  Purchase #2 $103.41   4.356%   $107.9145   $107.91   $107.90   $107.90  
  Purchase #3 $119.87   4.245%   $124.9585   $124.96   $124.95   $125.00  
  Purchase #4 $196.87   9.731%   $216.0274   $216.03   $216.05   $216.00  
  Purchase #5 $147.54   11.682%   $164.7756   $164.78   $164.80   $164.80  
  Purchase #6 $196.44   12.549%   $221.0913   $221.09   $221.10   $221.10  
  Purchase #7 $198.80   13.432%   $225.5028   $225.50   $225.50   $225.50  
  7 purchase totals = $1,138.48       $1,256.2752   $1,256.28   $1,256.30   $1,256.30