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 $231.72   5.159%   $243.6744   $243.67   $243.65   $243.70  
  Purchase #2 $88.81   6.406%   $94.4992   $94.50   $94.50   $94.50  
  Purchase #3 $140.52   4.245%   $146.4851   $146.49   $146.50   $146.50  
  Purchase #4 $56.93   10.774%   $63.0636   $63.06   $63.05   $63.10  
  Purchase #5 $183.78   5.665%   $194.1911   $194.19   $194.20   $194.20  
  Purchase #6 $117.49   12.782%   $132.5076   $132.51   $132.50   $132.50  
  Purchase #7 $68.59   9.627%   $75.1932   $75.19   $75.20   $75.20  
  7 purchase totals = $887.84       $949.6142   $949.61   $949.60   $949.70