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 $58.64   3.112%   $60.4649   $60.46   $60.45   $60.50  
  Purchase #2 $140.85   10.352%   $155.4308   $155.43   $155.45   $155.40  
  Purchase #3 $227.42   7.749%   $245.0428   $245.04   $245.05   $245.00  
  Purchase #4 $138.51   12.571%   $155.9221   $155.92   $155.90   $155.90  
  Purchase #5 $29.93   11.261%   $33.3004   $33.30   $33.30   $33.30  
  Purchase #6 $52.39   5.601%   $55.3244   $55.32   $55.30   $55.30  
  Purchase #7 $129.97   9.732%   $142.6187   $142.62   $142.60   $142.60  
  7 purchase totals = $777.71       $848.1041   $848.09   $848.05   $848.00