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 $66.85   13.614%   $75.951   $75.95   $75.95   $76.00  
  Purchase #2 $181.49   11.688%   $202.7026   $202.70   $202.70   $202.70  
  Purchase #3 $177.44   9.857%   $194.9303   $194.93   $194.95   $194.90  
  Purchase #4 $10.97   12.830%   $12.3775   $12.38   $12.40   $12.40  
  Purchase #5 $17.67   10.668%   $19.555   $19.56   $19.55   $19.60  
  Purchase #6 $21.32   5.261%   $22.4416   $22.44   $22.45   $22.40  
  Purchase #7 $130.30   9.332%   $142.4596   $142.46   $142.45   $142.50  
  7 purchase totals = $606.04       $670.4176   $670.42   $670.45   $670.50