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 $46.61   6.391%   $49.5888   $49.59   $49.60   $49.60  
  Purchase #2 $177.72   6.170%   $188.6853   $188.69   $188.70   $188.70  
  Purchase #3 $242.54   12.401%   $272.6174   $272.62   $272.60   $272.60  
  Purchase #4 $129.31   12.805%   $145.8681   $145.87   $145.85   $145.90  
  Purchase #5 $44.74   12.791%   $50.4627   $50.46   $50.45   $50.50  
  Purchase #6 $208.51   6.299%   $221.644   $221.64   $221.65   $221.60  
  Purchase #7 $31.88   12.390%   $35.8299   $35.83   $35.85   $35.80  
  7 purchase totals = $881.31       $964.6962   $964.70   $964.70   $964.70