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 $148.39   13.731%   $168.7654   $168.77   $168.75   $168.80  
  Purchase #2 $144.42   9.127%   $157.6012   $157.60   $157.60   $157.60  
  Purchase #3 $155.62   13.297%   $176.3128   $176.31   $176.30   $176.30  
  Purchase #4 $87.42   10.613%   $96.6979   $96.70   $96.70   $96.70  
  Purchase #5 $44.64   4.570%   $46.68   $46.68   $46.70   $46.70  
  Purchase #6 $136.57   9.674%   $149.7818   $149.78   $149.80   $149.80  
  Purchase #7 $197.68   13.566%   $224.4973   $224.50   $224.50   $224.50  
  7 purchase totals = $914.74       $1,020.3364   $1,020.34   $1,020.35   $1,020.40