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 $61.64   11.310%   $68.6115   $68.61   $68.60   $68.60  
  Purchase #2 $148.93   6.496%   $158.6045   $158.60   $158.60   $158.60  
  Purchase #3 $145.46   8.590%   $157.955   $157.96   $157.95   $158.00  
  Purchase #4 $109.83   5.847%   $116.2518   $116.25   $116.25   $116.30  
  Purchase #5 $40.93   8.409%   $44.3718   $44.37   $44.35   $44.40  
  Purchase #6 $94.40   11.320%   $105.0861   $105.09   $105.10   $105.10  
  Purchase #7 $132.26   9.120%   $144.3221   $144.32   $144.30   $144.30  
  7 purchase totals = $733.45       $795.2028   $795.20   $795.15   $795.30