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 $242.95   8.220%   $262.9205   $262.92   $262.90   $262.90  
  Purchase #2 $84.46   4.598%   $88.3435   $88.34   $88.35   $88.30  
  Purchase #3 $46.35   4.259%   $48.324   $48.32   $48.30   $48.30  
  Purchase #4 $56.31   7.401%   $60.4775   $60.48   $60.50   $60.50  
  Purchase #5 $241.69   6.395%   $257.1461   $257.15   $257.15   $257.10  
  Purchase #6 $110.88   13.241%   $125.5616   $125.56   $125.55   $125.60  
  Purchase #7 $160.73   7.493%   $172.7735   $172.77   $172.75   $172.80  
  7 purchase totals = $943.37       $1,015.5467   $1,015.54   $1,015.50   $1,015.50