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 $163.65   11.659%   $182.73   $182.73   $182.75   $182.70  
  Purchase #2 $97.26   11.306%   $108.2562   $108.26   $108.25   $108.30  
  Purchase #3 $58.44   5.221%   $61.4912   $61.49   $61.50   $61.50  
  Purchase #4 $217.97   7.486%   $234.2872   $234.29   $234.30   $234.30  
  Purchase #5 $16.25   3.122%   $16.7573   $16.76   $16.75   $16.80  
  Purchase #6 $71.25   4.668%   $74.576   $74.58   $74.60   $74.60  
  Purchase #7 $61.65   9.470%   $67.4883   $67.49   $67.50   $67.50  
  7 purchase totals = $686.47       $745.5862   $745.60   $745.65   $745.70