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 $217.93   13.357%   $247.0389   $247.04   $247.05   $247.00  
  Purchase #2 $62.65   11.342%   $69.7558   $69.76   $69.75   $69.80  
  Purchase #3 $82.54   11.787%   $92.269   $92.27   $92.25   $92.30  
  Purchase #4 $21.29   4.570%   $22.263   $22.26   $22.25   $22.30  
  Purchase #5 $170.90   3.457%   $176.808   $176.81   $176.80   $176.80  
  Purchase #6 $81.78   8.546%   $88.7689   $88.77   $88.75   $88.80  
  Purchase #7 $232.82   13.671%   $264.6488   $264.65   $264.65   $264.60  
  7 purchase totals = $869.91       $961.5524   $961.56   $961.50   $961.60