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 $217.75   13.543%   $247.2399   $247.24   $247.25   $247.20  
  Purchase #2 $155.57   13.370%   $176.3697   $176.37   $176.35   $176.40  
  Purchase #3 $218.77   13.796%   $248.9515   $248.95   $248.95   $249.00  
  Purchase #4 $19.69   13.325%   $22.3137   $22.31   $22.30   $22.30  
  Purchase #5 $204.87   8.838%   $222.9764   $222.98   $223.00   $223.00  
  Purchase #6 $63.69   9.269%   $69.5934   $69.59   $69.60   $69.60  
  Purchase #7 $104.96   6.114%   $111.3773   $111.38   $111.40   $111.40  
  7 purchase totals = $985.30       $1,098.8219   $1,098.82   $1,098.85   $1,098.90