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 $34.47   11.696%   $38.5016   $38.50   $38.50   $38.50  
  Purchase #2 $80.40   6.151%   $85.3454   $85.35   $85.35   $85.30  
  Purchase #3 $97.35   7.474%   $104.6259   $104.63   $104.65   $104.60  
  Purchase #4 $216.36   7.486%   $232.5567   $232.56   $232.55   $232.60  
  Purchase #5 $152.93   13.730%   $173.9273   $173.93   $173.95   $173.90  
  Purchase #6 $184.44   5.529%   $194.6377   $194.64   $194.65   $194.60  
  Purchase #7 $190.99   7.217%   $204.7737   $204.77   $204.75   $204.80  
  7 purchase totals = $956.94       $1,034.3683   $1,034.38   $1,034.40   $1,034.30