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 $164.46   13.732%   $187.0436   $187.04   $187.05   $187.00  
  Purchase #2 $243.95   13.247%   $276.2661   $276.27   $276.25   $276.30  
  Purchase #3 $107.44   4.832%   $112.6315   $112.63   $112.65   $112.60  
  Purchase #4 $132.55   3.496%   $137.1839   $137.18   $137.20   $137.20  
  Purchase #5 $187.69   8.290%   $203.2495   $203.25   $203.25   $203.20  
  Purchase #6 $88.45   7.295%   $94.9024   $94.90   $94.90   $94.90  
  Purchase #7 $192.59   13.280%   $218.166   $218.17   $218.15   $218.20  
  7 purchase totals = $1,117.13       $1,229.4430   $1,229.44   $1,229.45   $1,229.40