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 $184.85   9.661%   $202.7084   $202.71   $202.70   $202.70  
  Purchase #2 $76.29   12.161%   $85.5676   $85.57   $85.55   $85.60  
  Purchase #3 $65.52   12.267%   $73.5573   $73.56   $73.55   $73.60  
  Purchase #4 $232.56   4.583%   $243.2182   $243.22   $243.20   $243.20  
  Purchase #5 $160.72   3.405%   $166.1925   $166.19   $166.20   $166.20  
  Purchase #6 $131.30   13.409%   $148.906   $148.91   $148.90   $148.90  
  Purchase #7 $70.96   6.733%   $75.7377   $75.74   $75.75   $75.70  
  7 purchase totals = $922.20       $995.8877   $995.90   $995.85   $995.90