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 $221.83   10.594%   $245.3307   $245.33   $245.35   $245.30  
  Purchase #2 $72.66   7.314%   $77.9744   $77.97   $77.95   $78.00  
  Purchase #3 $98.40   8.349%   $106.6154   $106.62   $106.60   $106.60  
  Purchase #4 $150.47   9.767%   $165.1664   $165.17   $165.15   $165.20  
  Purchase #5 $18.99   3.793%   $19.7103   $19.71   $19.70   $19.70  
  Purchase #6 $96.55   11.559%   $107.7102   $107.71   $107.70   $107.70  
  Purchase #7 $101.79   8.545%   $110.488   $110.49   $110.50   $110.50  
  7 purchase totals = $760.69       $832.9954   $833.00   $832.95   $833.00