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 $15.49   6.783%   $16.5407   $16.54   $16.55   $16.50  
  Purchase #2 $188.27   9.240%   $205.6661   $205.67   $205.65   $205.70  
  Purchase #3 $52.67   5.487%   $55.56   $55.56   $55.55   $55.60  
  Purchase #4 $85.49   9.207%   $93.3611   $93.36   $93.35   $93.40  
  Purchase #5 $70.98   5.475%   $74.8662   $74.87   $74.85   $74.90  
  Purchase #6 $194.40   5.865%   $205.8016   $205.80   $205.80   $205.80  
  Purchase #7 $113.78   8.695%   $123.6732   $123.67   $123.65   $123.70  
  7 purchase totals = $721.08       $775.4689   $775.47   $775.40   $775.60