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 $216.43   8.153%   $234.0755   $234.08   $234.10   $234.10  
  Purchase #2 $242.99   8.164%   $262.8277   $262.83   $262.85   $262.80  
  Purchase #3 $59.81   10.406%   $66.0338   $66.03   $66.05   $66.00  
  Purchase #4 $78.48   8.154%   $84.8793   $84.88   $84.90   $84.90  
  Purchase #5 $103.84   11.190%   $115.4597   $115.46   $115.45   $115.50  
  Purchase #6 $241.67   8.486%   $262.1781   $262.18   $262.20   $262.20  
  Purchase #7 $47.93   12.475%   $53.9093   $53.91   $53.90   $53.90  
  7 purchase totals = $991.15       $1,079.3634   $1,079.37   $1,079.45   $1,079.40