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 $162.94   12.621%   $183.5047   $183.50   $183.50   $183.50  
  Purchase #2 $69.30   13.567%   $78.7019   $78.70   $78.70   $78.70  
  Purchase #3 $234.39   9.534%   $256.7367   $256.74   $256.75   $256.70  
  Purchase #4 $25.46   4.344%   $26.566   $26.57   $26.55   $26.60  
  Purchase #5 $132.74   11.755%   $148.3436   $148.34   $148.35   $148.30  
  Purchase #6 $223.72   7.149%   $239.7137   $239.71   $239.70   $239.70  
  Purchase #7 $58.64   8.858%   $63.8343   $63.83   $63.85   $63.80  
  7 purchase totals = $907.19       $997.4009   $997.39   $997.40   $997.30