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 $227.47   11.548%   $253.7382   $253.74   $253.75   $253.70  
  Purchase #2 $127.71   5.111%   $134.2373   $134.24   $134.25   $134.20  
  Purchase #3 $209.53   10.130%   $230.7554   $230.76   $230.75   $230.80  
  Purchase #4 $156.41   9.497%   $171.2643   $171.26   $171.25   $171.30  
  Purchase #5 $193.37   9.199%   $211.1581   $211.16   $211.15   $211.20  
  Purchase #6 $169.40   4.268%   $176.63   $176.63   $176.65   $176.60  
  Purchase #7 $57.96   11.121%   $64.4057   $64.41   $64.40   $64.40  
  7 purchase totals = $1,141.85       $1,242.1890   $1,242.20   $1,242.20   $1,242.20