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 $109.52   9.306%   $119.7119   $119.71   $119.70   $119.70  
  Purchase #2 $112.93   11.724%   $126.1699   $126.17   $126.15   $126.20  
  Purchase #3 $239.70   7.270%   $257.1262   $257.13   $257.15   $257.10  
  Purchase #4 $158.90   5.366%   $167.4266   $167.43   $167.45   $167.40  
  Purchase #5 $107.34   9.442%   $117.475   $117.48   $117.50   $117.50  
  Purchase #6 $59.59   8.760%   $64.8101   $64.81   $64.80   $64.80  
  Purchase #7 $31.26   5.259%   $32.904   $32.90   $32.90   $32.90  
  7 purchase totals = $819.24       $885.6237   $885.63   $885.65   $885.60