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 $113.68   8.871%   $123.7646   $123.76   $123.75   $123.80  
  Purchase #2 $174.55   8.835%   $189.9715   $189.97   $189.95   $190.00  
  Purchase #3 $231.77   11.637%   $258.7411   $258.74   $258.75   $258.70  
  Purchase #4 $82.95   11.672%   $92.6319   $92.63   $92.65   $92.60  
  Purchase #5 $207.68   5.622%   $219.3558   $219.36   $219.35   $219.40  
  Purchase #6 $56.53   12.164%   $63.4063   $63.41   $63.40   $63.40  
  Purchase #7 $17.95   9.177%   $19.5973   $19.60   $19.60   $19.60  
  7 purchase totals = $885.11       $967.4685   $967.47   $967.45   $967.50