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 $103.60   7.138%   $110.995   $111.00   $111.00   $111.00  
  Purchase #2 $95.72   8.365%   $103.727   $103.73   $103.75   $103.70  
  Purchase #3 $136.66   9.731%   $149.9584   $149.96   $149.95   $150.00  
  Purchase #4 $127.71   8.263%   $138.2627   $138.26   $138.25   $138.30  
  Purchase #5 $231.83   4.243%   $241.6665   $241.67   $241.65   $241.70  
  Purchase #6 $152.37   8.857%   $165.8654   $165.87   $165.85   $165.90  
  Purchase #7 $34.73   5.795%   $36.7426   $36.74   $36.75   $36.70  
  7 purchase totals = $882.62       $947.2176   $947.23   $947.20   $947.30