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 $107.55   11.227%   $119.6246   $119.62   $119.60   $119.60  
  Purchase #2 $34.95   3.874%   $36.304   $36.30   $36.30   $36.30  
  Purchase #3 $160.84   3.432%   $166.36   $166.36   $166.35   $166.40  
  Purchase #4 $89.60   7.390%   $96.2214   $96.22   $96.20   $96.20  
  Purchase #5 $192.39   8.470%   $208.6854   $208.69   $208.70   $208.70  
  Purchase #6 $194.77   6.454%   $207.3405   $207.34   $207.35   $207.30  
  Purchase #7 $66.77   10.297%   $73.6453   $73.65   $73.65   $73.60  
  7 purchase totals = $846.87       $908.1812   $908.18   $908.15   $908.10