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 $75.97   9.391%   $83.1043   $83.10   $83.10   $83.10  
  Purchase #2 $243.61   13.406%   $276.2684   $276.27   $276.25   $276.30  
  Purchase #3 $54.37   6.246%   $57.766   $57.77   $57.75   $57.80  
  Purchase #4 $225.32   3.805%   $233.8934   $233.89   $233.90   $233.90  
  Purchase #5 $201.91   4.688%   $211.3755   $211.38   $211.40   $211.40  
  Purchase #6 $31.27   13.675%   $35.5462   $35.55   $35.55   $35.50  
  Purchase #7 $33.51   4.467%   $35.0069   $35.01   $35.00   $35.00  
  7 purchase totals = $865.96       $932.9607   $932.97   $932.95   $933.00