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 $11.71   5.328%   $12.3339   $12.33   $12.35   $12.30  
  Purchase #2 $56.58   5.628%   $59.7643   $59.76   $59.75   $59.80  
  Purchase #3 $104.64   11.354%   $116.5208   $116.52   $116.50   $116.50  
  Purchase #4 $181.74   8.459%   $197.1134   $197.11   $197.10   $197.10  
  Purchase #5 $250.75   4.703%   $262.5428   $262.54   $262.55   $262.50  
  Purchase #6 $68.56   9.842%   $75.3077   $75.31   $75.30   $75.30  
  Purchase #7 $65.47   5.326%   $68.9569   $68.96   $68.95   $69.00  
  7 purchase totals = $739.45       $792.5398   $792.53   $792.50   $792.50