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 $11.96   8.327%   $12.9559   $12.96   $12.95   $13.00  
  Purchase #2 $207.84   8.564%   $225.6394   $225.64   $225.65   $225.60  
  Purchase #3 $90.91   8.528%   $98.6628   $98.66   $98.65   $98.70  
  Purchase #4 $159.57   3.319%   $164.8661   $164.87   $164.85   $164.90  
  Purchase #5 $130.85   6.425%   $139.2571   $139.26   $139.25   $139.30  
  Purchase #6 $55.86   13.729%   $63.529   $63.53   $63.55   $63.50  
  Purchase #7 $29.54   6.772%   $31.5404   $31.54   $31.55   $31.50  
  7 purchase totals = $686.53       $736.4507   $736.46   $736.45   $736.50