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 $110.80   8.119%   $119.7959   $119.80   $119.80   $119.80  
  Purchase #2 $112.43   5.262%   $118.3461   $118.35   $118.35   $118.30  
  Purchase #3 $164.59   12.793%   $185.646   $185.65   $185.65   $185.60  
  Purchase #4 $210.68   4.429%   $220.011   $220.01   $220.00   $220.00  
  Purchase #5 $246.89   4.739%   $258.5901   $258.59   $258.60   $258.60  
  Purchase #6 $150.29   4.214%   $156.6232   $156.62   $156.60   $156.60  
  Purchase #7 $61.36   4.484%   $64.1114   $64.11   $64.10   $64.10  
  7 purchase totals = $1,057.04       $1,123.1237   $1,123.13   $1,123.10   $1,123.00