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 $147.36   12.354%   $165.5649   $165.56   $165.55   $165.60  
  Purchase #2 $214.72   8.515%   $233.0034   $233.00   $233.00   $233.00  
  Purchase #3 $180.35   10.445%   $199.1876   $199.19   $199.20   $199.20  
  Purchase #4 $130.53   13.137%   $147.6777   $147.68   $147.70   $147.70  
  Purchase #5 $24.89   6.836%   $26.5915   $26.59   $26.60   $26.60  
  Purchase #6 $161.48   11.225%   $179.6061   $179.61   $179.60   $179.60  
  Purchase #7 $140.26   5.727%   $148.2927   $148.29   $148.30   $148.30  
  7 purchase totals = $999.59       $1,099.9239   $1,099.92   $1,099.95   $1,100.00