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 $248.56   7.296%   $266.6949   $266.69   $266.70   $266.70  
  Purchase #2 $99.87   6.243%   $106.1049   $106.10   $106.10   $106.10  
  Purchase #3 $51.88   10.144%   $57.1427   $57.14   $57.15   $57.10  
  Purchase #4 $81.66   11.529%   $91.0746   $91.07   $91.05   $91.10  
  Purchase #5 $192.62   7.665%   $207.3843   $207.38   $207.40   $207.40  
  Purchase #6 $85.86   10.334%   $94.7328   $94.73   $94.75   $94.70  
  Purchase #7 $203.58   8.329%   $220.5362   $220.54   $220.55   $220.50  
  7 purchase totals = $964.03       $1,043.6704   $1,043.65   $1,043.70   $1,043.60