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 $88.73   8.536%   $96.304   $96.30   $96.30   $96.30  
  Purchase #2 $46.25   8.637%   $50.2446   $50.24   $50.25   $50.20  
  Purchase #3 $217.63   8.271%   $235.6302   $235.63   $235.65   $235.60  
  Purchase #4 $113.25   5.605%   $119.5977   $119.60   $119.60   $119.60  
  Purchase #5 $246.78   10.658%   $273.0818   $273.08   $273.10   $273.10  
  Purchase #6 $93.69   5.679%   $99.0107   $99.01   $99.00   $99.00  
  Purchase #7 $166.60   11.644%   $185.9989   $186.00   $186.00   $186.00  
  7 purchase totals = $972.93       $1,059.8679   $1,059.86   $1,059.90   $1,059.80