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 $59.47   11.761%   $66.4643   $66.46   $66.45   $66.50  
  Purchase #2 $225.61   3.482%   $233.4657   $233.47   $233.45   $233.50  
  Purchase #3 $177.68   13.511%   $201.6863   $201.69   $201.70   $201.70  
  Purchase #4 $245.35   7.397%   $263.4985   $263.50   $263.50   $263.50  
  Purchase #5 $9.97   11.665%   $11.133   $11.13   $11.15   $11.10  
  Purchase #6 $105.75   3.776%   $109.7431   $109.74   $109.75   $109.70  
  Purchase #7 $33.49   6.564%   $35.6883   $35.69   $35.70   $35.70  
  7 purchase totals = $857.32       $921.6792   $921.68   $921.70   $921.70