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 $239.55   12.627%   $269.798   $269.80   $269.80   $269.80  
  Purchase #2 $136.48   4.228%   $142.2504   $142.25   $142.25   $142.30  
  Purchase #3 $246.31   12.601%   $277.3475   $277.35   $277.35   $277.30  
  Purchase #4 $162.45   7.189%   $174.1285   $174.13   $174.15   $174.10  
  Purchase #5 $94.27   11.204%   $104.832   $104.83   $104.85   $104.80  
  Purchase #6 $31.75   13.823%   $36.1388   $36.14   $36.15   $36.10  
  Purchase #7 $27.25   13.614%   $30.9598   $30.96   $30.95   $31.00  
  7 purchase totals = $938.06       $1,035.4550   $1,035.46   $1,035.50   $1,035.40