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 $24.42   8.636%   $26.5289   $26.53   $26.55   $26.50  
  Purchase #2 $193.62   6.301%   $205.82   $205.82   $205.80   $205.80  
  Purchase #3 $239.62   5.793%   $253.5012   $253.50   $253.50   $253.50  
  Purchase #4 $67.88   5.380%   $71.5319   $71.53   $71.55   $71.50  
  Purchase #5 $87.69   7.201%   $94.0046   $94.00   $94.00   $94.00  
  Purchase #6 $62.83   3.858%   $65.254   $65.25   $65.25   $65.30  
  Purchase #7 $206.51   9.380%   $225.8806   $225.88   $225.90   $225.90  
  7 purchase totals = $882.57       $942.5212   $942.51   $942.55   $942.50