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 $248.59   10.312%   $274.2246   $274.22   $274.20   $274.20  
  Purchase #2 $99.54   5.674%   $105.1879   $105.19   $105.20   $105.20  
  Purchase #3 $237.27   6.753%   $253.2928   $253.29   $253.30   $253.30  
  Purchase #4 $26.56   4.804%   $27.8359   $27.84   $27.85   $27.80  
  Purchase #5 $41.72   9.613%   $45.7305   $45.73   $45.75   $45.70  
  Purchase #6 $198.52   6.498%   $211.4198   $211.42   $211.40   $211.40  
  Purchase #7 $243.65   6.808%   $260.2377   $260.24   $260.25   $260.20  
  7 purchase totals = $1,095.85       $1,177.9292   $1,177.93   $1,177.95   $1,177.80