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 $195.46   4.475%   $204.2068   $204.21   $204.20   $204.20  
  Purchase #2 $93.72   10.291%   $103.3647   $103.36   $103.35   $103.40  
  Purchase #3 $151.66   6.738%   $161.8789   $161.88   $161.90   $161.90  
  Purchase #4 $159.43   4.491%   $166.59   $166.59   $166.60   $166.60  
  Purchase #5 $88.66   8.482%   $96.1801   $96.18   $96.20   $96.20  
  Purchase #6 $53.36   6.866%   $57.0237   $57.02   $57.00   $57.00  
  Purchase #7 $115.64   6.815%   $123.5209   $123.52   $123.50   $123.50  
  7 purchase totals = $857.93       $912.7651   $912.76   $912.75   $912.80