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 $241.49   11.438%   $269.1116   $269.11   $269.10   $269.10  
  Purchase #2 $112.85   5.255%   $118.7803   $118.78   $118.80   $118.80  
  Purchase #3 $80.32   5.409%   $84.6645   $84.66   $84.65   $84.70  
  Purchase #4 $247.82   8.142%   $267.9975   $268.00   $268.00   $268.00  
  Purchase #5 $244.39   6.798%   $261.0036   $261.00   $261.00   $261.00  
  Purchase #6 $124.31   9.341%   $135.9218   $135.92   $135.90   $135.90  
  Purchase #7 $159.63   4.115%   $166.1988   $166.20   $166.20   $166.20  
  7 purchase totals = $1,210.81       $1,303.6781   $1,303.67   $1,303.65   $1,303.70