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 $101.46   11.121%   $112.7434   $112.74   $112.75   $112.70  
  Purchase #2 $203.26   7.232%   $217.9598   $217.96   $217.95   $218.00  
  Purchase #3 $68.28   5.398%   $71.9658   $71.97   $71.95   $72.00  
  Purchase #4 $247.92   8.826%   $269.8014   $269.80   $269.80   $269.80  
  Purchase #5 $95.41   6.768%   $101.8673   $101.87   $101.85   $101.90  
  Purchase #6 $26.30   13.871%   $29.9481   $29.95   $29.95   $29.90  
  Purchase #7 $195.43   3.389%   $202.0531   $202.05   $202.05   $202.10  
  7 purchase totals = $938.06       $1,006.3389   $1,006.34   $1,006.30   $1,006.40