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 $217.36   10.196%   $239.522   $239.52   $239.50   $239.50  
  Purchase #2 $113.34   11.363%   $126.2188   $126.22   $126.20   $126.20  
  Purchase #3 $166.87   8.452%   $180.9739   $180.97   $180.95   $181.00  
  Purchase #4 $125.54   3.743%   $130.239   $130.24   $130.25   $130.20  
  Purchase #5 $162.55   7.490%   $174.725   $174.73   $174.75   $174.70  
  Purchase #6 $64.98   7.390%   $69.782   $69.78   $69.80   $69.80  
  Purchase #7 $113.89   7.296%   $122.1994   $122.20   $122.20   $122.20  
  7 purchase totals = $964.53       $1,043.6601   $1,043.66   $1,043.65   $1,043.60