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 $58.63   10.789%   $64.9556   $64.96   $64.95   $65.00  
  Purchase #2 $214.49   9.387%   $234.6242   $234.62   $234.60   $234.60  
  Purchase #3 $62.32   6.267%   $66.2256   $66.23   $66.25   $66.20  
  Purchase #4 $160.65   3.414%   $166.1346   $166.13   $166.15   $166.10  
  Purchase #5 $30.78   8.368%   $33.3557   $33.36   $33.35   $33.40  
  Purchase #6 $238.45   4.364%   $248.856   $248.86   $248.85   $248.90  
  Purchase #7 $223.92   5.814%   $236.9387   $236.94   $236.95   $236.90  
  7 purchase totals = $989.24       $1,051.0904   $1,051.10   $1,051.10   $1,051.10