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 $147.27   12.608%   $165.8378   $165.84   $165.85   $165.80  
  Purchase #2 $23.85   9.793%   $26.1856   $26.19   $26.20   $26.20  
  Purchase #3 $117.85   12.137%   $132.1535   $132.15   $132.15   $132.20  
  Purchase #4 $220.91   7.690%   $237.898   $237.90   $237.90   $237.90  
  Purchase #5 $224.76   6.325%   $238.9761   $238.98   $239.00   $239.00  
  Purchase #6 $18.61   7.591%   $20.0227   $20.02   $20.00   $20.00  
  Purchase #7 $56.39   9.212%   $61.5846   $61.58   $61.60   $61.60  
  7 purchase totals = $809.64       $882.6583   $882.66   $882.70   $882.70