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 $35.53   5.828%   $37.6007   $37.60   $37.60   $37.60  
  Purchase #2 $114.88   6.199%   $122.0014   $122.00   $122.00   $122.00  
  Purchase #3 $246.43   7.685%   $265.3681   $265.37   $265.35   $265.40  
  Purchase #4 $147.62   10.563%   $163.2131   $163.21   $163.20   $163.20  
  Purchase #5 $237.31   8.478%   $257.4291   $257.43   $257.45   $257.40  
  Purchase #6 $13.99   5.102%   $14.7038   $14.70   $14.70   $14.70  
  Purchase #7 $119.36   6.743%   $127.4084   $127.41   $127.40   $127.40  
  7 purchase totals = $915.12       $987.7246   $987.72   $987.70   $987.70