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 $186.94   8.413%   $202.6673   $202.67   $202.65   $202.70  
  Purchase #2 $146.54   11.205%   $162.9598   $162.96   $162.95   $163.00  
  Purchase #3 $216.91   5.646%   $229.1567   $229.16   $229.15   $229.20  
  Purchase #4 $249.45   10.219%   $274.9413   $274.94   $274.95   $274.90  
  Purchase #5 $184.62   9.549%   $202.2494   $202.25   $202.25   $202.20  
  Purchase #6 $125.45   4.553%   $131.1617   $131.16   $131.15   $131.20  
  Purchase #7 $154.82   4.661%   $162.0362   $162.04   $162.05   $162.00  
  7 purchase totals = $1,264.73       $1,365.1724   $1,365.18   $1,365.15   $1,365.20