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 $221.97   7.211%   $237.9763   $237.98   $238.00   $238.00  
  Purchase #2 $68.33   4.207%   $71.2046   $71.20   $71.20   $71.20  
  Purchase #3 $142.58   9.203%   $155.7016   $155.70   $155.70   $155.70  
  Purchase #4 $222.85   13.462%   $252.8501   $252.85   $252.85   $252.90  
  Purchase #5 $234.92   9.618%   $257.5146   $257.51   $257.50   $257.50  
  Purchase #6 $188.73   5.448%   $199.012   $199.01   $199.00   $199.00  
  Purchase #7 $159.62   6.208%   $169.5292   $169.53   $169.55   $169.50  
  7 purchase totals = $1,239.00       $1,343.7884   $1,343.78   $1,343.80   $1,343.80