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 $167.52   11.175%   $186.2404   $186.24   $186.25   $186.20  
  Purchase #2 $43.74   10.295%   $48.243   $48.24   $48.25   $48.20  
  Purchase #3 $50.82   6.322%   $54.0328   $54.03   $54.05   $54.00  
  Purchase #4 $82.54   12.289%   $92.6833   $92.68   $92.70   $92.70  
  Purchase #5 $159.64   5.558%   $168.5128   $168.51   $168.50   $168.50  
  Purchase #6 $185.78   9.383%   $203.2117   $203.21   $203.20   $203.20  
  Purchase #7 $204.64   6.300%   $217.5323   $217.53   $217.55   $217.50  
  7 purchase totals = $894.68       $970.4563   $970.44   $970.50   $970.30