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 $64.93   6.257%   $68.9927   $68.99   $69.00   $69.00  
  Purchase #2 $143.47   12.319%   $161.1441   $161.14   $161.15   $161.10  
  Purchase #3 $226.43   4.451%   $236.5084   $236.51   $236.50   $236.50  
  Purchase #4 $151.74   6.254%   $161.2298   $161.23   $161.25   $161.20  
  Purchase #5 $146.99   11.495%   $163.8865   $163.89   $163.90   $163.90  
  Purchase #6 $119.70   11.203%   $133.11   $133.11   $133.10   $133.10  
  Purchase #7 $195.73   4.496%   $204.53   $204.53   $204.55   $204.50  
  7 purchase totals = $1,048.99       $1,129.4015   $1,129.40   $1,129.45   $1,129.30