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 $23.69   4.241%   $24.6947   $24.69   $24.70   $24.70  
  Purchase #2 $60.68   4.393%   $63.3457   $63.35   $63.35   $63.30  
  Purchase #3 $161.79   3.466%   $167.3976   $167.40   $167.40   $167.40  
  Purchase #4 $56.94   5.180%   $59.8895   $59.89   $59.90   $59.90  
  Purchase #5 $12.70   12.752%   $14.3195   $14.32   $14.30   $14.30  
  Purchase #6 $59.82   6.718%   $63.8387   $63.84   $63.85   $63.80  
  Purchase #7 $86.73   7.636%   $93.3527   $93.35   $93.35   $93.40  
  7 purchase totals = $462.35       $486.8384   $486.84   $486.85   $486.80