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 $216.54   4.534%   $226.3579   $226.36   $226.35   $226.40  
  Purchase #2 $244.32   13.695%   $277.7796   $277.78   $277.80   $277.80  
  Purchase #3 $162.35   7.148%   $173.9548   $173.95   $173.95   $174.00  
  Purchase #4 $241.49   13.184%   $273.328   $273.33   $273.35   $273.30  
  Purchase #5 $183.26   10.467%   $202.4418   $202.44   $202.45   $202.40  
  Purchase #6 $30.55   12.547%   $34.3831   $34.38   $34.40   $34.40  
  Purchase #7 $247.51   9.180%   $270.2314   $270.23   $270.25   $270.20  
  7 purchase totals = $1,326.02       $1,458.4766   $1,458.47   $1,458.55   $1,458.50