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 $205.69   6.450%   $218.957   $218.96   $218.95   $219.00  
  Purchase #2 $38.99   8.492%   $42.301   $42.30   $42.30   $42.30  
  Purchase #3 $54.28   12.615%   $61.1274   $61.13   $61.15   $61.10  
  Purchase #4 $118.42   4.430%   $123.666   $123.67   $123.65   $123.70  
  Purchase #5 $239.37   4.410%   $249.9262   $249.93   $249.95   $249.90  
  Purchase #6 $61.50   13.291%   $69.674   $69.67   $69.65   $69.70  
  Purchase #7 $46.72   9.508%   $51.1621   $51.16   $51.15   $51.20  
  7 purchase totals = $764.97       $816.8137   $816.82   $816.80   $816.90