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 $126.98   12.571%   $142.9427   $142.94   $142.95   $142.90  
  Purchase #2 $150.61   8.646%   $163.6317   $163.63   $163.65   $163.60  
  Purchase #3 $119.64   11.824%   $133.7862   $133.79   $133.80   $133.80  
  Purchase #4 $241.42   5.300%   $254.2153   $254.22   $254.20   $254.20  
  Purchase #5 $63.44   13.502%   $72.0057   $72.01   $72.00   $72.00  
  Purchase #6 $32.89   4.602%   $34.4036   $34.40   $34.40   $34.40  
  Purchase #7 $247.39   13.788%   $281.5001   $281.50   $281.50   $281.50  
  7 purchase totals = $982.37       $1,082.4853   $1,082.49   $1,082.50   $1,082.40