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 $24.67   3.589%   $25.5554   $25.56   $25.55   $25.60  
  Purchase #2 $185.29   13.157%   $209.6686   $209.67   $209.65   $209.70  
  Purchase #3 $47.96   10.262%   $52.8817   $52.88   $52.90   $52.90  
  Purchase #4 $206.52   3.870%   $214.5123   $214.51   $214.50   $214.50  
  Purchase #5 $242.75   13.296%   $275.026   $275.03   $275.05   $275.00  
  Purchase #6 $61.29   11.668%   $68.4413   $68.44   $68.45   $68.40  
  Purchase #7 $86.74   6.833%   $92.6669   $92.67   $92.65   $92.70  
  7 purchase totals = $855.22       $938.7522   $938.76   $938.75   $938.80