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 $115.41   10.605%   $127.6492   $127.65   $127.65   $127.60  
  Purchase #2 $9.86   11.392%   $10.9833   $10.98   $11.00   $11.00  
  Purchase #3 $202.99   13.643%   $230.6839   $230.68   $230.70   $230.70  
  Purchase #4 $179.36   6.122%   $190.3404   $190.34   $190.35   $190.30  
  Purchase #5 $140.29   13.406%   $159.0973   $159.10   $159.10   $159.10  
  Purchase #6 $187.60   6.158%   $199.1524   $199.15   $199.15   $199.20  
  Purchase #7 $86.83   8.546%   $94.2505   $94.25   $94.25   $94.30  
  7 purchase totals = $922.34       $1,012.1570   $1,012.15   $1,012.20   $1,012.20