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 $73.94   12.174%   $82.9415   $82.94   $82.95   $82.90  
  Purchase #2 $250.99   10.527%   $277.4117   $277.41   $277.40   $277.40  
  Purchase #3 $244.64   3.425%   $253.0189   $253.02   $253.00   $253.00  
  Purchase #4 $93.33   3.579%   $96.6703   $96.67   $96.65   $96.70  
  Purchase #5 $105.95   9.306%   $115.8097   $115.81   $115.80   $115.80  
  Purchase #6 $222.70   13.546%   $252.8669   $252.87   $252.85   $252.90  
  Purchase #7 $240.55   10.168%   $265.0091   $265.01   $265.00   $265.00  
  7 purchase totals = $1,232.10       $1,343.7281   $1,343.73   $1,343.65   $1,343.70