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 $208.94   11.517%   $233.0036   $233.00   $233.00   $233.00  
  Purchase #2 $80.42   6.757%   $85.854   $85.85   $85.85   $85.90  
  Purchase #3 $162.44   9.346%   $177.6216   $177.62   $177.60   $177.60  
  Purchase #4 $164.79   8.702%   $179.13   $179.13   $179.15   $179.10  
  Purchase #5 $62.82   9.557%   $68.8237   $68.82   $68.80   $68.80  
  Purchase #6 $113.69   12.625%   $128.0434   $128.04   $128.05   $128.00  
  Purchase #7 $22.70   4.281%   $23.6718   $23.67   $23.65   $23.70  
  7 purchase totals = $815.80       $896.1481   $896.13   $896.10   $896.10