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 $87.74   4.386%   $91.5883   $91.59   $91.60   $91.60  
  Purchase #2 $206.54   4.399%   $215.6257   $215.63   $215.65   $215.60  
  Purchase #3 $67.46   9.222%   $73.6812   $73.68   $73.70   $73.70  
  Purchase #4 $145.99   4.855%   $153.0778   $153.08   $153.10   $153.10  
  Purchase #5 $158.66   7.610%   $170.734   $170.73   $170.75   $170.70  
  Purchase #6 $75.98   3.749%   $78.8285   $78.83   $78.85   $78.80  
  Purchase #7 $170.96   12.403%   $192.1642   $192.16   $192.15   $192.20  
  7 purchase totals = $913.33       $975.6997   $975.70   $975.80   $975.70