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 $233.34   12.219%   $261.8518   $261.85   $261.85   $261.90  
  Purchase #2 $28.25   5.321%   $29.7532   $29.75   $29.75   $29.80  
  Purchase #3 $34.80   5.137%   $36.5877   $36.59   $36.60   $36.60  
  Purchase #4 $61.39   6.870%   $65.6075   $65.61   $65.60   $65.60  
  Purchase #5 $178.43   7.207%   $191.2895   $191.29   $191.30   $191.30  
  Purchase #6 $224.86   11.605%   $250.955   $250.96   $250.95   $251.00  
  Purchase #7 $26.41   6.760%   $28.1953   $28.20   $28.20   $28.20  
  7 purchase totals = $787.48       $864.2400   $864.25   $864.25   $864.40