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 $47.39   3.598%   $49.0951   $49.10   $49.10   $49.10  
  Purchase #2 $60.64   9.834%   $66.6033   $66.60   $66.60   $66.60  
  Purchase #3 $96.40   7.387%   $103.5211   $103.52   $103.50   $103.50  
  Purchase #4 $246.89   6.253%   $262.328   $262.33   $262.35   $262.30  
  Purchase #5 $132.65   3.631%   $137.4665   $137.47   $137.45   $137.50  
  Purchase #6 $199.83   3.703%   $207.2297   $207.23   $207.25   $207.20  
  Purchase #7 $91.45   7.872%   $98.6489   $98.65   $98.65   $98.60  
  7 purchase totals = $875.25       $924.8926   $924.90   $924.90   $924.80