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 $67.71   8.114%   $73.204   $73.20   $73.20   $73.20  
  Purchase #2 $244.82   13.286%   $277.3468   $277.35   $277.35   $277.30  
  Purchase #3 $225.58   12.108%   $252.8932   $252.89   $252.90   $252.90  
  Purchase #4 $11.52   6.676%   $12.2891   $12.29   $12.30   $12.30  
  Purchase #5 $131.48   4.238%   $137.0521   $137.05   $137.05   $137.10  
  Purchase #6 $245.77   3.739%   $254.9593   $254.96   $254.95   $255.00  
  Purchase #7 $185.64   4.417%   $193.8397   $193.84   $193.85   $193.80  
  7 purchase totals = $1,112.52       $1,201.5842   $1,201.58   $1,201.60   $1,201.60