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 $32.89   9.551%   $36.0313   $36.03   $36.05   $36.00  
  Purchase #2 $10.41   11.542%   $11.6115   $11.61   $11.60   $11.60  
  Purchase #3 $88.79   6.463%   $94.5285   $94.53   $94.55   $94.50  
  Purchase #4 $189.47   13.599%   $215.236   $215.24   $215.25   $215.20  
  Purchase #5 $63.57   3.595%   $65.8553   $65.86   $65.85   $65.90  
  Purchase #6 $229.67   12.284%   $257.8827   $257.88   $257.90   $257.90  
  Purchase #7 $198.66   7.742%   $214.0403   $214.04   $214.05   $214.00  
  7 purchase totals = $813.46       $895.1856   $895.19   $895.25   $895.10