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 $61.30   7.583%   $65.9484   $65.95   $65.95   $65.90  
  Purchase #2 $90.46   6.583%   $96.415   $96.42   $96.40   $96.40  
  Purchase #3 $70.99   10.846%   $78.6896   $78.69   $78.70   $78.70  
  Purchase #4 $147.78   12.746%   $166.616   $166.62   $166.60   $166.60  
  Purchase #5 $25.47   10.135%   $28.0514   $28.05   $28.05   $28.10  
  Purchase #6 $217.62   11.547%   $242.7486   $242.75   $242.75   $242.70  
  Purchase #7 $122.64   10.869%   $135.9697   $135.97   $135.95   $136.00  
  7 purchase totals = $736.26       $814.4387   $814.45   $814.40   $814.40