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 $56.97   5.464%   $60.0828   $60.08   $60.10   $60.10  
  Purchase #2 $210.56   11.770%   $235.3429   $235.34   $235.35   $235.30  
  Purchase #3 $7.39   12.633%   $8.3236   $8.32   $8.30   $8.30  
  Purchase #4 $248.79   10.860%   $275.8086   $275.81   $275.80   $275.80  
  Purchase #5 $35.40   5.241%   $37.2553   $37.26   $37.25   $37.30  
  Purchase #6 $111.65   12.437%   $125.5359   $125.54   $125.55   $125.50  
  Purchase #7 $193.69   12.578%   $218.0523   $218.05   $218.05   $218.10  
  7 purchase totals = $864.45       $960.4014   $960.40   $960.40   $960.40