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 $70.85   3.109%   $73.0527   $73.05   $73.05   $73.10  
  Purchase #2 $94.64   5.227%   $99.5868   $99.59   $99.60   $99.60  
  Purchase #3 $228.70   12.159%   $256.5076   $256.51   $256.50   $256.50  
  Purchase #4 $30.92   9.802%   $33.9508   $33.95   $33.95   $34.00  
  Purchase #5 $225.64   10.652%   $249.6752   $249.68   $249.70   $249.70  
  Purchase #6 $244.53   12.501%   $275.0987   $275.10   $275.10   $275.10  
  Purchase #7 $70.74   8.292%   $76.6058   $76.61   $76.60   $76.60  
  7 purchase totals = $966.02       $1,064.4776   $1,064.49   $1,064.50   $1,064.60