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 $125.68   3.849%   $130.5174   $130.52   $130.50   $130.50  
  Purchase #2 $98.57   3.171%   $101.6957   $101.70   $101.70   $101.70  
  Purchase #3 $8.44   11.653%   $9.4235   $9.42   $9.40   $9.40  
  Purchase #4 $194.91   5.736%   $206.09   $206.09   $206.10   $206.10  
  Purchase #5 $206.35   8.267%   $223.409   $223.41   $223.40   $223.40  
  Purchase #6 $126.81   7.730%   $136.6124   $136.61   $136.60   $136.60  
  Purchase #7 $40.60   10.502%   $44.8638   $44.86   $44.85   $44.90  
  7 purchase totals = $801.36       $852.6118   $852.61   $852.55   $852.60