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 $242.91   4.844%   $254.6766   $254.68   $254.70   $254.70  
  Purchase #2 $6.28   4.863%   $6.5854   $6.59   $6.60   $6.60  
  Purchase #3 $77.83   3.215%   $80.3322   $80.33   $80.35   $80.30  
  Purchase #4 $221.41   3.861%   $229.9586   $229.96   $229.95   $230.00  
  Purchase #5 $227.66   3.114%   $234.7493   $234.75   $234.75   $234.70  
  Purchase #6 $162.50   8.386%   $176.1273   $176.13   $176.15   $176.10  
  Purchase #7 $57.80   7.580%   $62.1812   $62.18   $62.20   $62.20  
  7 purchase totals = $996.39       $1,044.6106   $1,044.62   $1,044.70   $1,044.60