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 $212.84   10.243%   $234.6412   $234.64   $234.65   $234.60  
  Purchase #2 $5.97   12.141%   $6.6948   $6.69   $6.70   $6.70  
  Purchase #3 $163.46   4.260%   $170.4234   $170.42   $170.40   $170.40  
  Purchase #4 $116.87   4.677%   $122.336   $122.34   $122.35   $122.30  
  Purchase #5 $175.99   4.460%   $183.8392   $183.84   $183.85   $183.80  
  Purchase #6 $176.49   8.278%   $191.0998   $191.10   $191.10   $191.10  
  Purchase #7 $111.36   12.335%   $125.0963   $125.10   $125.10   $125.10  
  7 purchase totals = $962.98       $1,034.1307   $1,034.13   $1,034.15   $1,034.00