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 $39.32   5.503%   $41.4838   $41.48   $41.50   $41.50  
  Purchase #2 $135.97   3.373%   $140.5563   $140.56   $140.55   $140.60  
  Purchase #3 $236.88   6.824%   $253.0447   $253.04   $253.05   $253.00  
  Purchase #4 $126.78   13.762%   $144.2275   $144.23   $144.25   $144.20  
  Purchase #5 $153.93   4.239%   $160.4551   $160.46   $160.45   $160.50  
  Purchase #6 $48.31   13.765%   $54.9599   $54.96   $54.95   $55.00  
  Purchase #7 $236.31   13.847%   $269.0318   $269.03   $269.05   $269.00  
  7 purchase totals = $977.50       $1,063.7591   $1,063.76   $1,063.80   $1,063.80