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 $95.48   9.546%   $104.5945   $104.59   $104.60   $104.60  
  Purchase #2 $162.83   8.768%   $177.1069   $177.11   $177.10   $177.10  
  Purchase #3 $153.25   4.555%   $160.2305   $160.23   $160.25   $160.20  
  Purchase #4 $24.27   3.776%   $25.1864   $25.19   $25.20   $25.20  
  Purchase #5 $139.58   7.524%   $150.082   $150.08   $150.10   $150.10  
  Purchase #6 $192.94   5.178%   $202.9304   $202.93   $202.95   $202.90  
  Purchase #7 $104.34   6.866%   $111.504   $111.50   $111.50   $111.50  
  7 purchase totals = $872.69       $931.6347   $931.63   $931.70   $931.60