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 $69.37   10.802%   $76.8633   $76.86   $76.85   $76.90  
  Purchase #2 $188.85   8.403%   $204.7191   $204.72   $204.70   $204.70  
  Purchase #3 $186.96   7.257%   $200.5277   $200.53   $200.55   $200.50  
  Purchase #4 $141.78   8.193%   $153.396   $153.40   $153.40   $153.40  
  Purchase #5 $220.85   8.721%   $240.1103   $240.11   $240.10   $240.10  
  Purchase #6 $225.45   8.863%   $245.4316   $245.43   $245.45   $245.40  
  Purchase #7 $178.28   9.719%   $195.607   $195.61   $195.60   $195.60  
  7 purchase totals = $1,211.54       $1,316.6550   $1,316.66   $1,316.65   $1,316.60