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 $222.49   11.354%   $247.7515   $247.75   $247.75   $247.80  
  Purchase #2 $168.71   4.679%   $176.6039   $176.60   $176.60   $176.60  
  Purchase #3 $189.84   7.129%   $203.3737   $203.37   $203.35   $203.40  
  Purchase #4 $250.33   7.836%   $269.9459   $269.95   $269.95   $269.90  
  Purchase #5 $245.39   9.376%   $268.3978   $268.40   $268.40   $268.40  
  Purchase #6 $8.30   4.617%   $8.6832   $8.68   $8.70   $8.70  
  Purchase #7 $85.81   10.222%   $94.5815   $94.58   $94.60   $94.60  
  7 purchase totals = $1,170.87       $1,269.3375   $1,269.33   $1,269.35   $1,269.40