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 $60.42   7.174%   $64.7545   $64.75   $64.75   $64.80  
  Purchase #2 $44.27   12.163%   $49.6546   $49.65   $49.65   $49.70  
  Purchase #3 $188.61   5.173%   $198.3668   $198.37   $198.35   $198.40  
  Purchase #4 $185.31   13.619%   $210.5474   $210.55   $210.55   $210.50  
  Purchase #5 $211.37   5.739%   $223.5005   $223.50   $223.50   $223.50  
  Purchase #6 $211.93   6.865%   $226.479   $226.48   $226.50   $226.50  
  Purchase #7 $12.45   8.201%   $13.471   $13.47   $13.45   $13.50  
  7 purchase totals = $914.36       $986.7738   $986.77   $986.75   $986.90