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 $103.88   6.593%   $110.7288   $110.73   $110.75   $110.70  
  Purchase #2 $140.44   4.376%   $146.5857   $146.59   $146.60   $146.60  
  Purchase #3 $156.43   10.390%   $172.6831   $172.68   $172.70   $172.70  
  Purchase #4 $208.86   10.364%   $230.5063   $230.51   $230.50   $230.50  
  Purchase #5 $192.54   6.809%   $205.65   $205.65   $205.65   $205.70  
  Purchase #6 $72.42   5.544%   $76.435   $76.44   $76.45   $76.40  
  Purchase #7 $149.44   4.505%   $156.1723   $156.17   $156.15   $156.20  
  7 purchase totals = $1,024.01       $1,098.7612   $1,098.77   $1,098.80   $1,098.80