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 $243.39   10.173%   $268.1501   $268.15   $268.15   $268.20  
  Purchase #2 $147.53   13.808%   $167.9009   $167.90   $167.90   $167.90  
  Purchase #3 $70.90   4.798%   $74.3018   $74.30   $74.30   $74.30  
  Purchase #4 $194.57   3.808%   $201.9792   $201.98   $202.00   $202.00  
  Purchase #5 $98.77   6.769%   $105.4557   $105.46   $105.45   $105.50  
  Purchase #6 $21.25   11.466%   $23.6865   $23.69   $23.70   $23.70  
  Purchase #7 $37.80   11.560%   $42.1697   $42.17   $42.15   $42.20  
  7 purchase totals = $814.21       $883.6439   $883.65   $883.65   $883.80