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 $43.31   3.363%   $44.7665   $44.77   $44.75   $44.80  
  Purchase #2 $28.89   12.206%   $32.4163   $32.42   $32.40   $32.40  
  Purchase #3 $86.57   6.708%   $92.3771   $92.38   $92.40   $92.40  
  Purchase #4 $147.47   6.634%   $157.2532   $157.25   $157.25   $157.30  
  Purchase #5 $219.43   5.713%   $231.966   $231.97   $231.95   $232.00  
  Purchase #6 $55.76   6.689%   $59.4898   $59.49   $59.50   $59.50  
  Purchase #7 $198.97   7.644%   $214.1793   $214.18   $214.20   $214.20  
  7 purchase totals = $780.40       $832.4482   $832.46   $832.45   $832.60