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 $49.57   10.259%   $54.6554   $54.66   $54.65   $54.70  
  Purchase #2 $102.96   4.534%   $107.6282   $107.63   $107.65   $107.60  
  Purchase #3 $226.59   12.712%   $255.3941   $255.39   $255.40   $255.40  
  Purchase #4 $217.48   12.538%   $244.7476   $244.75   $244.75   $244.70  
  Purchase #5 $32.60   6.686%   $34.7796   $34.78   $34.80   $34.80  
  Purchase #6 $150.68   9.154%   $164.4732   $164.47   $164.45   $164.50  
  Purchase #7 $183.48   10.120%   $202.0482   $202.05   $202.05   $202.00  
  7 purchase totals = $963.36       $1,063.7263   $1,063.73   $1,063.75   $1,063.70