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 $84.91   10.344%   $93.6931   $93.69   $93.70   $93.70  
  Purchase #2 $56.62   8.798%   $61.6014   $61.60   $61.60   $61.60  
  Purchase #3 $188.58   10.779%   $208.907   $208.91   $208.90   $208.90  
  Purchase #4 $158.83   6.459%   $169.0888   $169.09   $169.10   $169.10  
  Purchase #5 $12.62   7.637%   $13.5838   $13.58   $13.60   $13.60  
  Purchase #6 $75.57   12.419%   $84.955   $84.96   $84.95   $85.00  
  Purchase #7 $226.69   11.614%   $253.0178   $253.02   $253.00   $253.00  
  7 purchase totals = $803.82       $884.8469   $884.85   $884.85   $884.90