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 $66.64   7.244%   $71.4674   $71.47   $71.45   $71.50  
  Purchase #2 $104.25   13.146%   $117.9547   $117.95   $117.95   $118.00  
  Purchase #3 $121.95   4.388%   $127.3012   $127.30   $127.30   $127.30  
  Purchase #4 $151.29   8.359%   $163.9363   $163.94   $163.95   $163.90  
  Purchase #5 $60.46   12.607%   $68.0822   $68.08   $68.10   $68.10  
  Purchase #6 $111.97   9.787%   $122.9285   $122.93   $122.95   $122.90  
  Purchase #7 $221.75   12.860%   $250.2671   $250.27   $250.25   $250.30  
  7 purchase totals = $838.31       $921.9374   $921.94   $921.95   $922.00