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 $247.85   8.757%   $269.5542   $269.55   $269.55   $269.60  
  Purchase #2 $246.32   13.330%   $279.1545   $279.15   $279.15   $279.20  
  Purchase #3 $60.86   10.658%   $67.3465   $67.35   $67.35   $67.30  
  Purchase #4 $179.62   5.457%   $189.4219   $189.42   $189.40   $189.40  
  Purchase #5 $199.30   11.152%   $221.5259   $221.53   $221.55   $221.50  
  Purchase #6 $51.39   7.583%   $55.2869   $55.29   $55.30   $55.30  
  Purchase #7 $23.91   8.622%   $25.9715   $25.97   $25.95   $26.00  
  7 purchase totals = $1,009.25       $1,108.2614   $1,108.26   $1,108.25   $1,108.30