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 $245.88   5.452%   $259.2854   $259.29   $259.30   $259.30  
  Purchase #2 $132.86   5.421%   $140.0623   $140.06   $140.05   $140.10  
  Purchase #3 $54.64   5.193%   $57.4775   $57.48   $57.50   $57.50  
  Purchase #4 $5.25   7.726%   $5.6556   $5.66   $5.65   $5.70  
  Purchase #5 $235.95   4.452%   $246.4545   $246.45   $246.45   $246.50  
  Purchase #6 $177.34   10.110%   $195.2691   $195.27   $195.25   $195.30  
  Purchase #7 $216.97   13.865%   $247.0529   $247.05   $247.05   $247.10  
  7 purchase totals = $1,068.89       $1,151.2573   $1,151.26   $1,151.25   $1,151.50