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 $71.61   4.672%   $74.9556   $74.96   $74.95   $75.00  
  Purchase #2 $107.31   8.314%   $116.2318   $116.23   $116.25   $116.20  
  Purchase #3 $103.82   6.730%   $110.8071   $110.81   $110.80   $110.80  
  Purchase #4 $243.38   6.268%   $258.6351   $258.64   $258.65   $258.60  
  Purchase #5 $201.88   5.172%   $212.3212   $212.32   $212.30   $212.30  
  Purchase #6 $173.79   11.214%   $193.2788   $193.28   $193.30   $193.30  
  Purchase #7 $184.67   10.866%   $204.7362   $204.74   $204.75   $204.70  
  7 purchase totals = $1,086.46       $1,170.9658   $1,170.98   $1,171.00   $1,170.90