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 $60.29   13.447%   $68.3972   $68.40   $68.40   $68.40  
  Purchase #2 $105.71   3.321%   $109.2206   $109.22   $109.20   $109.20  
  Purchase #3 $26.25   5.683%   $27.7418   $27.74   $27.75   $27.70  
  Purchase #4 $194.89   5.275%   $205.1704   $205.17   $205.15   $205.20  
  Purchase #5 $75.47   13.314%   $85.5181   $85.52   $85.50   $85.50  
  Purchase #6 $41.76   12.417%   $46.9453   $46.95   $46.95   $46.90  
  Purchase #7 $192.36   11.150%   $213.8081   $213.81   $213.80   $213.80  
  7 purchase totals = $696.73       $756.8015   $756.81   $756.75   $756.70