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 $154.82   6.388%   $164.7099   $164.71   $164.70   $164.70  
  Purchase #2 $28.52   8.332%   $30.8963   $30.90   $30.90   $30.90  
  Purchase #3 $193.39   4.443%   $201.9823   $201.98   $202.00   $202.00  
  Purchase #4 $70.74   7.254%   $75.8715   $75.87   $75.85   $75.90  
  Purchase #5 $119.97   6.660%   $127.96   $127.96   $127.95   $128.00  
  Purchase #6 $203.54   12.701%   $229.3916   $229.39   $229.40   $229.40  
  Purchase #7 $194.97   9.733%   $213.9464   $213.95   $213.95   $213.90  
  7 purchase totals = $965.95       $1,044.7580   $1,044.76   $1,044.75   $1,044.80