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 $204.74   4.663%   $214.287   $214.29   $214.30   $214.30  
  Purchase #2 $205.89   6.382%   $219.0299   $219.03   $219.05   $219.00  
  Purchase #3 $130.83   6.225%   $138.9742   $138.97   $138.95   $139.00  
  Purchase #4 $56.72   3.814%   $58.8833   $58.88   $58.90   $58.90  
  Purchase #5 $40.74   4.857%   $42.7187   $42.72   $42.70   $42.70  
  Purchase #6 $14.70   7.649%   $15.8244   $15.82   $15.80   $15.80  
  Purchase #7 $105.42   13.173%   $119.307   $119.31   $119.30   $119.30  
  7 purchase totals = $759.04       $809.0245   $809.02   $809.00   $809.00