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 $38.81   13.690%   $44.1231   $44.12   $44.10   $44.10  
  Purchase #2 $125.66   7.201%   $134.7088   $134.71   $134.70   $134.70  
  Purchase #3 $104.55   3.868%   $108.594   $108.59   $108.60   $108.60  
  Purchase #4 $204.71   3.811%   $212.5115   $212.51   $212.50   $212.50  
  Purchase #5 $176.74   10.817%   $195.858   $195.86   $195.85   $195.90  
  Purchase #6 $67.50   4.270%   $70.3823   $70.38   $70.40   $70.40  
  Purchase #7 $186.93   13.616%   $212.3824   $212.38   $212.40   $212.40  
  7 purchase totals = $904.90       $978.5601   $978.55   $978.55   $978.60