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 $156.41   8.148%   $169.1543   $169.15   $169.15   $169.20  
  Purchase #2 $177.59   13.196%   $201.0248   $201.02   $201.00   $201.00  
  Purchase #3 $195.91   10.377%   $216.2396   $216.24   $216.25   $216.20  
  Purchase #4 $33.38   9.480%   $36.5444   $36.54   $36.55   $36.50  
  Purchase #5 $168.47   4.575%   $176.1775   $176.18   $176.20   $176.20  
  Purchase #6 $79.28   13.452%   $89.9447   $89.94   $89.95   $89.90  
  Purchase #7 $115.32   11.572%   $128.6648   $128.66   $128.65   $128.70  
  7 purchase totals = $926.36       $1,017.7501   $1,017.73   $1,017.75   $1,017.70