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 $76.49   7.391%   $82.1434   $82.14   $82.15   $82.10  
  Purchase #2 $33.74   5.515%   $35.6008   $35.60   $35.60   $35.60  
  Purchase #3 $71.68   10.219%   $79.005   $79.01   $79.00   $79.00  
  Purchase #4 $194.25   13.385%   $220.2504   $220.25   $220.25   $220.30  
  Purchase #5 $193.52   6.419%   $205.942   $205.94   $205.95   $205.90  
  Purchase #6 $204.89   6.259%   $217.7141   $217.71   $217.70   $217.70  
  Purchase #7 $121.49   7.203%   $130.2409   $130.24   $130.25   $130.20  
  7 purchase totals = $896.06       $970.8966   $970.89   $970.90   $970.80