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 $119.74   3.557%   $123.9992   $124.00   $124.00   $124.00  
  Purchase #2 $5.58   12.239%   $6.2629   $6.26   $6.25   $6.30  
  Purchase #3 $56.84   7.108%   $60.8802   $60.88   $60.90   $60.90  
  Purchase #4 $234.90   4.210%   $244.7893   $244.79   $244.80   $244.80  
  Purchase #5 $107.69   10.704%   $119.2171   $119.22   $119.20   $119.20  
  Purchase #6 $117.39   13.765%   $133.5487   $133.55   $133.55   $133.50  
  Purchase #7 $154.31   12.753%   $173.9892   $173.99   $174.00   $174.00  
  7 purchase totals = $796.45       $862.6866   $862.69   $862.70   $862.70