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 $246.92   5.493%   $260.4833   $260.48   $260.50   $260.50  
  Purchase #2 $226.39   8.463%   $245.5494   $245.55   $245.55   $245.50  
  Purchase #3 $79.65   6.224%   $84.6074   $84.61   $84.60   $84.60  
  Purchase #4 $163.53   3.500%   $169.2536   $169.25   $169.25   $169.30  
  Purchase #5 $74.28   6.228%   $78.9062   $78.91   $78.90   $78.90  
  Purchase #6 $207.37   10.295%   $228.7187   $228.72   $228.70   $228.70  
  Purchase #7 $39.79   10.862%   $44.112   $44.11   $44.10   $44.10  
  7 purchase totals = $1,037.93       $1,111.6306   $1,111.63   $1,111.60   $1,111.60