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 $54.67   6.568%   $58.2607   $58.26   $58.25   $58.30  
  Purchase #2 $115.71   6.359%   $123.068   $123.07   $123.05   $123.10  
  Purchase #3 $185.89   10.797%   $205.9605   $205.96   $205.95   $206.00  
  Purchase #4 $31.32   9.210%   $34.2046   $34.20   $34.20   $34.20  
  Purchase #5 $81.38   9.796%   $89.352   $89.35   $89.35   $89.40  
  Purchase #6 $183.80   6.288%   $195.3573   $195.36   $195.35   $195.40  
  Purchase #7 $61.88   3.263%   $63.8991   $63.90   $63.90   $63.90  
  7 purchase totals = $714.65       $770.1022   $770.10   $770.05   $770.30