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 $68.94   10.596%   $76.2449   $76.24   $76.25   $76.20  
  Purchase #2 $123.96   4.476%   $129.5084   $129.51   $129.50   $129.50  
  Purchase #3 $115.63   3.490%   $119.6655   $119.67   $119.65   $119.70  
  Purchase #4 $120.33   10.442%   $132.8949   $132.89   $132.90   $132.90  
  Purchase #5 $191.78   13.129%   $216.9588   $216.96   $216.95   $217.00  
  Purchase #6 $196.84   12.636%   $221.7127   $221.71   $221.70   $221.70  
  Purchase #7 $110.59   11.554%   $123.3676   $123.37   $123.35   $123.40  
  7 purchase totals = $928.07       $1,020.3528   $1,020.35   $1,020.30   $1,020.40