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 $84.66   11.499%   $94.3951   $94.40   $94.40   $94.40  
  Purchase #2 $181.51   5.554%   $191.5911   $191.59   $191.60   $191.60  
  Purchase #3 $130.88   9.789%   $143.6918   $143.69   $143.70   $143.70  
  Purchase #4 $117.57   7.874%   $126.8275   $126.83   $126.85   $126.80  
  Purchase #5 $25.70   7.377%   $27.5959   $27.60   $27.60   $27.60  
  Purchase #6 $156.29   4.617%   $163.5059   $163.51   $163.50   $163.50  
  Purchase #7 $70.85   4.701%   $74.1807   $74.18   $74.20   $74.20  
  7 purchase totals = $767.46       $821.7880   $821.80   $821.85   $821.80