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 $227.49   13.311%   $257.7712   $257.77   $257.75   $257.80  
  Purchase #2 $249.74   8.537%   $271.0603   $271.06   $271.05   $271.10  
  Purchase #3 $247.96   13.538%   $281.5288   $281.53   $281.55   $281.50  
  Purchase #4 $166.87   9.597%   $182.8845   $182.88   $182.90   $182.90  
  Purchase #5 $94.49   13.856%   $107.5825   $107.58   $107.60   $107.60  
  Purchase #6 $219.42   5.217%   $230.8671   $230.87   $230.85   $230.90  
  Purchase #7 $245.34   6.237%   $260.6419   $260.64   $260.65   $260.60  
  7 purchase totals = $1,451.31       $1,592.3363   $1,592.33   $1,592.35   $1,592.40