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 $71.63   8.344%   $77.6068   $77.61   $77.60   $77.60  
  Purchase #2 $209.68   8.216%   $226.9073   $226.91   $226.90   $226.90  
  Purchase #3 $125.49   7.724%   $135.1828   $135.18   $135.20   $135.20  
  Purchase #4 $190.55   4.519%   $199.161   $199.16   $199.15   $199.20  
  Purchase #5 $211.66   3.582%   $219.2417   $219.24   $219.25   $219.20  
  Purchase #6 $23.85   5.855%   $25.2464   $25.25   $25.25   $25.20  
  Purchase #7 $173.82   6.429%   $184.9949   $184.99   $185.00   $185.00  
  7 purchase totals = $1,006.68       $1,068.3409   $1,068.34   $1,068.35   $1,068.30