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 $116.42   13.749%   $132.4266   $132.43   $132.45   $132.40  
  Purchase #2 $87.82   8.343%   $95.1468   $95.15   $95.15   $95.10  
  Purchase #3 $227.26   11.383%   $253.129   $253.13   $253.15   $253.10  
  Purchase #4 $47.34   13.375%   $53.6717   $53.67   $53.65   $53.70  
  Purchase #5 $59.99   5.626%   $63.365   $63.37   $63.35   $63.40  
  Purchase #6 $249.33   6.635%   $265.873   $265.87   $265.85   $265.90  
  Purchase #7 $159.70   6.771%   $170.5133   $170.51   $170.50   $170.50  
  7 purchase totals = $947.86       $1,034.1254   $1,034.13   $1,034.10   $1,034.10