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 $24.41   11.204%   $27.1449   $27.14   $27.15   $27.10  
  Purchase #2 $103.71   9.655%   $113.7232   $113.72   $113.70   $113.70  
  Purchase #3 $214.34   7.224%   $229.8239   $229.82   $229.80   $229.80  
  Purchase #4 $164.26   7.184%   $176.0604   $176.06   $176.05   $176.10  
  Purchase #5 $97.74   7.376%   $104.9493   $104.95   $104.95   $104.90  
  Purchase #6 $229.95   10.463%   $254.0097   $254.01   $254.00   $254.00  
  Purchase #7 $19.57   6.787%   $20.8982   $20.90   $20.90   $20.90  
  7 purchase totals = $853.98       $926.6096   $926.60   $926.55   $926.50