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 $249.55   3.276%   $257.7253   $257.73   $257.75   $257.70  
  Purchase #2 $243.62   9.343%   $266.3814   $266.38   $266.40   $266.40  
  Purchase #3 $28.58   13.177%   $32.346   $32.35   $32.35   $32.30  
  Purchase #4 $8.51   4.121%   $8.8607   $8.86   $8.85   $8.90  
  Purchase #5 $88.79   6.426%   $94.4956   $94.50   $94.50   $94.50  
  Purchase #6 $163.88   5.523%   $172.9311   $172.93   $172.95   $172.90  
  Purchase #7 $202.27   8.633%   $219.732   $219.73   $219.75   $219.70  
  7 purchase totals = $985.20       $1,052.4721   $1,052.48   $1,052.55   $1,052.40