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 $63.39   13.171%   $71.7391   $71.74   $71.75   $71.70  
  Purchase #2 $141.42   3.280%   $146.0586   $146.06   $146.05   $146.10  
  Purchase #3 $106.89   13.401%   $121.2143   $121.21   $121.20   $121.20  
  Purchase #4 $170.81   11.516%   $190.4805   $190.48   $190.50   $190.50  
  Purchase #5 $245.42   5.512%   $258.9476   $258.95   $258.95   $258.90  
  Purchase #6 $236.45   11.718%   $264.1572   $264.16   $264.15   $264.20  
  Purchase #7 $9.99   7.588%   $10.748   $10.75   $10.75   $10.70  
  7 purchase totals = $974.37       $1,063.3453   $1,063.35   $1,063.35   $1,063.30