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 $39.61   4.343%   $41.3303   $41.33   $41.35   $41.30  
  Purchase #2 $93.73   8.371%   $101.5761   $101.58   $101.60   $101.60  
  Purchase #3 $192.66   8.292%   $208.6354   $208.64   $208.65   $208.60  
  Purchase #4 $210.78   11.506%   $235.0323   $235.03   $235.05   $235.00  
  Purchase #5 $116.49   12.674%   $131.2539   $131.25   $131.25   $131.30  
  Purchase #6 $130.63   4.487%   $136.4914   $136.49   $136.50   $136.50  
  Purchase #7 $202.76   12.433%   $227.9692   $227.97   $227.95   $228.00  
  7 purchase totals = $986.66       $1,082.2886   $1,082.29   $1,082.35   $1,082.30