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 $162.49   11.369%   $180.9635   $180.96   $180.95   $181.00  
  Purchase #2 $84.83   12.730%   $95.6289   $95.63   $95.65   $95.60  
  Purchase #3 $195.28   12.872%   $220.4164   $220.42   $220.40   $220.40  
  Purchase #4 $181.29   6.152%   $192.443   $192.44   $192.45   $192.40  
  Purchase #5 $223.90   5.302%   $235.7712   $235.77   $235.75   $235.80  
  Purchase #6 $244.65   3.783%   $253.9051   $253.91   $253.90   $253.90  
  Purchase #7 $166.83   12.792%   $188.1709   $188.17   $188.15   $188.20  
  7 purchase totals = $1,259.27       $1,367.2990   $1,367.30   $1,367.25   $1,367.30