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 $220.37   12.656%   $248.26   $248.26   $248.25   $248.30  
  Purchase #2 $96.84   10.363%   $106.8755   $106.88   $106.90   $106.90  
  Purchase #3 $78.39   3.553%   $81.1752   $81.18   $81.20   $81.20  
  Purchase #4 $241.81   12.206%   $271.3253   $271.33   $271.35   $271.30  
  Purchase #5 $28.27   5.172%   $29.7321   $29.73   $29.75   $29.70  
  Purchase #6 $85.46   11.175%   $95.0102   $95.01   $95.00   $95.00  
  Purchase #7 $83.80   7.851%   $90.3791   $90.38   $90.40   $90.40  
  7 purchase totals = $834.94       $922.7574   $922.77   $922.85   $922.80