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 $61.68   8.212%   $66.7452   $66.75   $66.75   $66.70  
  Purchase #2 $54.79   13.248%   $62.0486   $62.05   $62.05   $62.00  
  Purchase #3 $10.75   11.671%   $12.0046   $12.00   $12.00   $12.00  
  Purchase #4 $16.34   8.508%   $17.7302   $17.73   $17.75   $17.70  
  Purchase #5 $218.65   13.864%   $248.9636   $248.96   $248.95   $249.00  
  Purchase #6 $206.80   13.569%   $234.8607   $234.86   $234.85   $234.90  
  Purchase #7 $145.54   5.530%   $153.5884   $153.59   $153.60   $153.60  
  7 purchase totals = $714.55       $795.9413   $795.94   $795.95   $795.90