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 $228.44   8.402%   $247.6335   $247.63   $247.65   $247.60  
  Purchase #2 $85.73   10.160%   $94.4402   $94.44   $94.45   $94.40  
  Purchase #3 $140.51   10.382%   $155.0977   $155.10   $155.10   $155.10  
  Purchase #4 $24.64   11.363%   $27.4398   $27.44   $27.45   $27.40  
  Purchase #5 $125.51   7.162%   $134.499   $134.50   $134.50   $134.50  
  Purchase #6 $244.97   7.279%   $262.8014   $262.80   $262.80   $262.80  
  Purchase #7 $228.80   8.827%   $248.9962   $249.00   $249.00   $249.00  
  7 purchase totals = $1,078.60       $1,170.9078   $1,170.91   $1,170.95   $1,170.80