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 $11.37   3.787%   $11.8006   $11.80   $11.80   $11.80  
  Purchase #2 $44.68   4.520%   $46.6995   $46.70   $46.70   $46.70  
  Purchase #3 $198.65   10.581%   $219.6692   $219.67   $219.65   $219.70  
  Purchase #4 $46.54   12.154%   $52.1965   $52.20   $52.20   $52.20  
  Purchase #5 $22.27   3.161%   $22.974   $22.97   $22.95   $23.00  
  Purchase #6 $249.99   10.452%   $276.119   $276.12   $276.10   $276.10  
  Purchase #7 $178.44   5.283%   $187.867   $187.87   $187.85   $187.90  
  7 purchase totals = $751.94       $817.3258   $817.33   $817.25   $817.40