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 $232.46   6.742%   $248.1325   $248.13   $248.15   $248.10  
  Purchase #2 $214.39   12.393%   $240.9594   $240.96   $240.95   $241.00  
  Purchase #3 $106.67   6.443%   $113.5427   $113.54   $113.55   $113.50  
  Purchase #4 $171.99   3.112%   $177.3423   $177.34   $177.35   $177.30  
  Purchase #5 $74.46   13.747%   $84.696   $84.70   $84.70   $84.70  
  Purchase #6 $233.98   9.256%   $255.6372   $255.64   $255.65   $255.60  
  Purchase #7 $71.33   7.665%   $76.7974   $76.80   $76.80   $76.80  
  7 purchase totals = $1,105.28       $1,197.1075   $1,197.11   $1,197.15   $1,197.00