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 $37.34   11.466%   $41.6214   $41.62   $41.60   $41.60  
  Purchase #2 $205.87   8.173%   $222.6958   $222.70   $222.70   $222.70  
  Purchase #3 $146.76   13.649%   $166.7913   $166.79   $166.80   $166.80  
  Purchase #4 $246.47   12.627%   $277.5918   $277.59   $277.60   $277.60  
  Purchase #5 $188.86   4.683%   $197.7043   $197.70   $197.70   $197.70  
  Purchase #6 $58.48   5.492%   $61.6917   $61.69   $61.70   $61.70  
  Purchase #7 $237.97   3.270%   $245.7516   $245.75   $245.75   $245.80  
  7 purchase totals = $1,121.75       $1,213.8479   $1,213.84   $1,213.85   $1,213.90