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 $49.75   10.469%   $54.9583   $54.96   $54.95   $55.00  
  Purchase #2 $162.48   6.867%   $173.6375   $173.64   $173.65   $173.60  
  Purchase #3 $244.27   9.669%   $267.8885   $267.89   $267.90   $267.90  
  Purchase #4 $92.54   11.560%   $103.2376   $103.24   $103.25   $103.20  
  Purchase #5 $218.66   7.380%   $234.7971   $234.80   $234.80   $234.80  
  Purchase #6 $27.47   9.139%   $29.9805   $29.98   $30.00   $30.00  
  Purchase #7 $120.32   13.660%   $136.7557   $136.76   $136.75   $136.80  
  7 purchase totals = $915.49       $1,001.2552   $1,001.27   $1,001.30   $1,001.30