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 $238.66   12.348%   $268.1297   $268.13   $268.15   $268.10  
  Purchase #2 $29.57   4.312%   $30.8451   $30.85   $30.85   $30.80  
  Purchase #3 $166.95   3.363%   $172.5645   $172.56   $172.55   $172.60  
  Purchase #4 $66.27   6.580%   $70.6306   $70.63   $70.65   $70.60  
  Purchase #5 $43.92   11.674%   $49.0472   $49.05   $49.05   $49.00  
  Purchase #6 $125.85   4.623%   $131.668   $131.67   $131.65   $131.70  
  Purchase #7 $163.40   9.798%   $179.4099   $179.41   $179.40   $179.40  
  7 purchase totals = $834.62       $902.2950   $902.30   $902.30   $902.20