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 $51.96   4.609%   $54.3548   $54.35   $54.35   $54.40  
  Purchase #2 $204.71   10.332%   $225.8606   $225.86   $225.85   $225.90  
  Purchase #3 $236.71   13.250%   $268.0741   $268.07   $268.05   $268.10  
  Purchase #4 $161.64   8.231%   $174.9446   $174.94   $174.95   $174.90  
  Purchase #5 $162.84   5.154%   $171.2328   $171.23   $171.25   $171.20  
  Purchase #6 $158.71   8.798%   $172.6733   $172.67   $172.65   $172.70  
  Purchase #7 $154.92   3.417%   $160.2136   $160.21   $160.20   $160.20  
  7 purchase totals = $1,131.49       $1,227.3538   $1,227.33   $1,227.30   $1,227.40