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 $73.55   3.561%   $76.1691   $76.17   $76.15   $76.20  
  Purchase #2 $213.88   6.156%   $227.0465   $227.05   $227.05   $227.00  
  Purchase #3 $154.88   6.372%   $164.749   $164.75   $164.75   $164.70  
  Purchase #4 $243.97   9.614%   $267.4253   $267.43   $267.45   $267.40  
  Purchase #5 $49.78   6.543%   $53.0371   $53.04   $53.05   $53.00  
  Purchase #6 $31.46   6.192%   $33.408   $33.41   $33.40   $33.40  
  Purchase #7 $13.25   8.176%   $14.3333   $14.33   $14.35   $14.30  
  7 purchase totals = $780.77       $836.1683   $836.18   $836.20   $836.00