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 $242.51   10.492%   $267.9541   $267.95   $267.95   $268.00  
  Purchase #2 $104.42   8.410%   $113.2017   $113.20   $113.20   $113.20  
  Purchase #3 $230.71   10.255%   $254.3693   $254.37   $254.35   $254.40  
  Purchase #4 $205.81   7.322%   $220.8794   $220.88   $220.90   $220.90  
  Purchase #5 $64.34   6.831%   $68.7351   $68.74   $68.75   $68.70  
  Purchase #6 $13.71   9.728%   $15.0437   $15.04   $15.05   $15.00  
  Purchase #7 $73.77   11.372%   $82.1591   $82.16   $82.15   $82.20  
  7 purchase totals = $935.27       $1,022.3424   $1,022.34   $1,022.35   $1,022.40