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 $43.57   6.378%   $46.3489   $46.35   $46.35   $46.30  
  Purchase #2 $163.75   6.634%   $174.6132   $174.61   $174.60   $174.60  
  Purchase #3 $211.37   6.177%   $224.4263   $224.43   $224.45   $224.40  
  Purchase #4 $217.47   5.203%   $228.785   $228.79   $228.80   $228.80  
  Purchase #5 $124.29   9.400%   $135.9733   $135.97   $135.95   $136.00  
  Purchase #6 $219.78   9.645%   $240.9778   $240.98   $241.00   $241.00  
  Purchase #7 $193.60   8.142%   $209.3629   $209.36   $209.35   $209.40  
  7 purchase totals = $1,173.83       $1,260.4874   $1,260.49   $1,260.50   $1,260.50