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 $67.60   8.491%   $73.3399   $73.34   $73.35   $73.30  
  Purchase #2 $50.49   7.806%   $54.4312   $54.43   $54.45   $54.40  
  Purchase #3 $91.66   12.357%   $102.9864   $102.99   $103.00   $103.00  
  Purchase #4 $248.25   8.250%   $268.7306   $268.73   $268.75   $268.70  
  Purchase #5 $238.98   13.764%   $271.8732   $271.87   $271.85   $271.90  
  Purchase #6 $230.53   6.662%   $245.8879   $245.89   $245.90   $245.90  
  Purchase #7 $137.42   12.690%   $154.8586   $154.86   $154.85   $154.90  
  7 purchase totals = $1,064.93       $1,172.1078   $1,172.11   $1,172.15   $1,172.10