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 $71.65   10.126%   $78.9053   $78.91   $78.90   $78.90  
  Purchase #2 $168.97   8.654%   $183.5927   $183.59   $183.60   $183.60  
  Purchase #3 $35.74   6.334%   $38.0038   $38.00   $38.00   $38.00  
  Purchase #4 $181.95   11.179%   $202.2902   $202.29   $202.30   $202.30  
  Purchase #5 $245.29   9.329%   $268.1731   $268.17   $268.15   $268.20  
  Purchase #6 $225.46   9.621%   $247.1515   $247.15   $247.15   $247.20  
  Purchase #7 $242.32   4.534%   $253.3068   $253.31   $253.30   $253.30  
  7 purchase totals = $1,171.38       $1,271.4234   $1,271.42   $1,271.40   $1,271.50