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 $194.93   11.342%   $217.039   $217.04   $217.05   $217.00  
  Purchase #2 $62.26   8.509%   $67.5577   $67.56   $67.55   $67.60  
  Purchase #3 $243.39   12.109%   $272.8621   $272.86   $272.85   $272.90  
  Purchase #4 $169.45   4.358%   $176.8346   $176.83   $176.85   $176.80  
  Purchase #5 $134.25   10.447%   $148.2751   $148.28   $148.30   $148.30  
  Purchase #6 $56.50   10.141%   $62.2297   $62.23   $62.25   $62.20  
  Purchase #7 $174.48   5.440%   $183.9717   $183.97   $183.95   $184.00  
  7 purchase totals = $1,035.26       $1,128.7699   $1,128.77   $1,128.80   $1,128.80