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 $53.51   9.613%   $58.6539   $58.65   $58.65   $58.70  
  Purchase #2 $192.92   6.766%   $205.973   $205.97   $205.95   $206.00  
  Purchase #3 $54.51   9.257%   $59.556   $59.56   $59.55   $59.60  
  Purchase #4 $51.62   10.393%   $56.9849   $56.98   $57.00   $57.00  
  Purchase #5 $23.43   10.719%   $25.9415   $25.94   $25.95   $25.90  
  Purchase #6 $122.36   5.508%   $129.0996   $129.10   $129.10   $129.10  
  Purchase #7 $86.77   10.662%   $96.0214   $96.02   $96.00   $96.00  
  7 purchase totals = $585.12       $632.2303   $632.22   $632.20   $632.30