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 $211.65   5.673%   $223.6569   $223.66   $223.65   $223.70  
  Purchase #2 $235.38   10.598%   $260.3256   $260.33   $260.35   $260.30  
  Purchase #3 $60.60   9.370%   $66.2782   $66.28   $66.30   $66.30  
  Purchase #4 $132.57   3.635%   $137.3889   $137.39   $137.40   $137.40  
  Purchase #5 $76.41   13.848%   $86.9913   $86.99   $87.00   $87.00  
  Purchase #6 $13.90   5.300%   $14.6367   $14.64   $14.65   $14.60  
  Purchase #7 $194.50   10.384%   $214.6969   $214.70   $214.70   $214.70  
  7 purchase totals = $925.01       $1,003.9745   $1,003.99   $1,004.05   $1,004.00