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 $105.93   7.341%   $113.7063   $113.71   $113.70   $113.70  
  Purchase #2 $149.79   6.112%   $158.9452   $158.95   $158.95   $158.90  
  Purchase #3 $56.44   12.126%   $63.2839   $63.28   $63.30   $63.30  
  Purchase #4 $73.60   3.508%   $76.1819   $76.18   $76.20   $76.20  
  Purchase #5 $12.92   12.552%   $14.5417   $14.54   $14.55   $14.50  
  Purchase #6 $116.72   3.207%   $120.4632   $120.46   $120.45   $120.50  
  Purchase #7 $211.76   5.272%   $222.924   $222.92   $222.90   $222.90  
  7 purchase totals = $727.16       $770.0462   $770.04   $770.05   $770.00