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 $205.95   8.728%   $223.9253   $223.93   $223.95   $223.90  
  Purchase #2 $112.90   13.226%   $127.8322   $127.83   $127.85   $127.80  
  Purchase #3 $100.95   4.732%   $105.727   $105.73   $105.75   $105.70  
  Purchase #4 $156.51   8.497%   $169.8087   $169.81   $169.80   $169.80  
  Purchase #5 $49.25   6.382%   $52.3931   $52.39   $52.40   $52.40  
  Purchase #6 $142.79   13.347%   $161.8482   $161.85   $161.85   $161.80  
  Purchase #7 $226.79   8.488%   $246.0399   $246.04   $246.05   $246.00  
  7 purchase totals = $995.14       $1,087.5744   $1,087.58   $1,087.65   $1,087.40