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 $106.58   11.622%   $118.9667   $118.97   $118.95   $119.00  
  Purchase #2 $31.40   6.345%   $33.3923   $33.39   $33.40   $33.40  
  Purchase #3 $138.61   9.152%   $151.2956   $151.30   $151.30   $151.30  
  Purchase #4 $156.32   11.207%   $173.8388   $173.84   $173.85   $173.80  
  Purchase #5 $178.49   4.798%   $187.054   $187.05   $187.05   $187.10  
  Purchase #6 $72.82   4.370%   $76.0022   $76.00   $76.00   $76.00  
  Purchase #7 $233.90   8.761%   $254.392   $254.39   $254.40   $254.40  
  7 purchase totals = $918.12       $994.9416   $994.94   $994.95   $995.00