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 $221.97   10.623%   $245.5499   $245.55   $245.55   $245.50  
  Purchase #2 $35.80   11.526%   $39.9263   $39.93   $39.95   $39.90  
  Purchase #3 $68.66   4.746%   $71.9186   $71.92   $71.90   $71.90  
  Purchase #4 $224.78   9.630%   $246.4263   $246.43   $246.45   $246.40  
  Purchase #5 $153.38   8.861%   $166.971   $166.97   $166.95   $167.00  
  Purchase #6 $28.50   13.508%   $32.3498   $32.35   $32.35   $32.30  
  Purchase #7 $245.28   10.342%   $270.6469   $270.65   $270.65   $270.60  
  7 purchase totals = $978.37       $1,073.7888   $1,073.80   $1,073.80   $1,073.60