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 $69.61   3.212%   $71.8459   $71.85   $71.85   $71.80  
  Purchase #2 $178.87   13.744%   $203.4539   $203.45   $203.45   $203.50  
  Purchase #3 $93.46   4.646%   $97.8022   $97.80   $97.80   $97.80  
  Purchase #4 $249.40   10.406%   $275.3526   $275.35   $275.35   $275.40  
  Purchase #5 $187.40   6.459%   $199.5042   $199.50   $199.50   $199.50  
  Purchase #6 $42.34   5.836%   $44.811   $44.81   $44.80   $44.80  
  Purchase #7 $155.92   10.296%   $171.9735   $171.97   $171.95   $172.00  
  7 purchase totals = $977.00       $1,064.7433   $1,064.73   $1,064.70   $1,064.80