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 $61.88   8.803%   $67.3273   $67.33   $67.35   $67.30  
  Purchase #2 $28.84   3.209%   $29.7655   $29.77   $29.75   $29.80  
  Purchase #3 $229.83   6.227%   $244.1415   $244.14   $244.15   $244.10  
  Purchase #4 $202.67   9.398%   $221.7169   $221.72   $221.70   $221.70  
  Purchase #5 $8.47   3.536%   $8.7695   $8.77   $8.75   $8.80  
  Purchase #6 $83.49   4.444%   $87.2003   $87.20   $87.20   $87.20  
  Purchase #7 $249.31   3.847%   $258.901   $258.90   $258.90   $258.90  
  7 purchase totals = $864.49       $917.8220   $917.83   $917.80   $917.80