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 $87.31   11.723%   $97.5454   $97.55   $97.55   $97.50  
  Purchase #2 $162.54   9.138%   $177.3929   $177.39   $177.40   $177.40  
  Purchase #3 $245.46   4.422%   $256.3142   $256.31   $256.30   $256.30  
  Purchase #4 $166.33   3.555%   $172.243   $172.24   $172.25   $172.20  
  Purchase #5 $136.36   12.784%   $153.7923   $153.79   $153.80   $153.80  
  Purchase #6 $191.77   5.533%   $202.3806   $202.38   $202.40   $202.40  
  Purchase #7 $155.52   13.529%   $176.5603   $176.56   $176.55   $176.60  
  7 purchase totals = $1,145.29       $1,236.2287   $1,236.22   $1,236.25   $1,236.20