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 $56.58   13.260%   $64.0825   $64.08   $64.10   $64.10  
  Purchase #2 $38.64   6.610%   $41.1941   $41.19   $41.20   $41.20  
  Purchase #3 $162.41   9.601%   $178.003   $178.00   $178.00   $178.00  
  Purchase #4 $86.77   13.201%   $98.2245   $98.22   $98.20   $98.20  
  Purchase #5 $119.27   6.618%   $127.1633   $127.16   $127.15   $127.20  
  Purchase #6 $141.42   4.790%   $148.194   $148.19   $148.20   $148.20  
  Purchase #7 $239.43   12.686%   $269.8041   $269.80   $269.80   $269.80  
  7 purchase totals = $844.52       $926.6655   $926.64   $926.65   $926.70