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 $69.77   6.652%   $74.4111   $74.41   $74.40   $74.40  
  Purchase #2 $100.89   13.345%   $114.3538   $114.35   $114.35   $114.40  
  Purchase #3 $119.67   4.219%   $124.7189   $124.72   $124.70   $124.70  
  Purchase #4 $56.26   11.290%   $62.6118   $62.61   $62.60   $62.60  
  Purchase #5 $250.97   10.135%   $276.4058   $276.41   $276.40   $276.40  
  Purchase #6 $146.49   13.691%   $166.5459   $166.55   $166.55   $166.50  
  Purchase #7 $184.36   11.110%   $204.8424   $204.84   $204.85   $204.80  
  7 purchase totals = $928.41       $1,023.8897   $1,023.89   $1,023.85   $1,023.80