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 $56.50   11.806%   $63.1704   $63.17   $63.15   $63.20  
  Purchase #2 $192.82   4.267%   $201.0476   $201.05   $201.05   $201.00  
  Purchase #3 $14.60   7.204%   $15.6518   $15.65   $15.65   $15.70  
  Purchase #4 $131.68   12.480%   $148.1137   $148.11   $148.10   $148.10  
  Purchase #5 $208.90   8.299%   $226.2366   $226.24   $226.25   $226.20  
  Purchase #6 $249.88   8.436%   $270.9599   $270.96   $270.95   $271.00  
  Purchase #7 $34.68   4.155%   $36.121   $36.12   $36.10   $36.10  
  7 purchase totals = $889.06       $961.3010   $961.30   $961.25   $961.30