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 $198.37   4.214%   $206.7293   $206.73   $206.75   $206.70  
  Purchase #2 $118.31   11.819%   $132.2931   $132.29   $132.30   $132.30  
  Purchase #3 $174.37   3.612%   $180.6682   $180.67   $180.65   $180.70  
  Purchase #4 $163.64   6.452%   $174.1981   $174.20   $174.20   $174.20  
  Purchase #5 $53.75   6.572%   $57.2825   $57.28   $57.30   $57.30  
  Purchase #6 $64.89   13.835%   $73.8675   $73.87   $73.85   $73.90  
  Purchase #7 $7.75   5.698%   $8.1916   $8.19   $8.20   $8.20  
  7 purchase totals = $781.08       $833.2303   $833.23   $833.25   $833.30