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 $23.83   13.140%   $26.9613   $26.96   $26.95   $27.00  
  Purchase #2 $171.86   11.311%   $191.2991   $191.30   $191.30   $191.30  
  Purchase #3 $13.51   3.337%   $13.9608   $13.96   $13.95   $14.00  
  Purchase #4 $8.99   8.769%   $9.7783   $9.78   $9.80   $9.80  
  Purchase #5 $162.98   9.233%   $178.0279   $178.03   $178.05   $178.00  
  Purchase #6 $83.90   11.250%   $93.3388   $93.34   $93.35   $93.30  
  Purchase #7 $241.75   11.491%   $269.5295   $269.53   $269.55   $269.50  
  7 purchase totals = $706.82       $782.8957   $782.90   $782.95   $782.90