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 $68.49   8.299%   $74.174   $74.17   $74.15   $74.20  
  Purchase #2 $179.46   9.392%   $196.3149   $196.31   $196.30   $196.30  
  Purchase #3 $217.77   7.778%   $234.7082   $234.71   $234.70   $234.70  
  Purchase #4 $75.80   8.180%   $82.0004   $82.00   $82.00   $82.00  
  Purchase #5 $156.29   12.347%   $175.5871   $175.59   $175.60   $175.60  
  Purchase #6 $194.99   12.123%   $218.6286   $218.63   $218.65   $218.60  
  Purchase #7 $76.32   10.437%   $84.2855   $84.29   $84.30   $84.30  
  7 purchase totals = $969.12       $1,065.6987   $1,065.70   $1,065.70   $1,065.70