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 $187.65   9.606%   $205.6757   $205.68   $205.70   $205.70  
  Purchase #2 $48.61   7.118%   $52.0701   $52.07   $52.05   $52.10  
  Purchase #3 $198.54   10.692%   $219.7679   $219.77   $219.75   $219.80  
  Purchase #4 $142.62   11.653%   $159.2395   $159.24   $159.25   $159.20  
  Purchase #5 $241.61   3.247%   $249.4551   $249.46   $249.45   $249.50  
  Purchase #6 $43.34   6.321%   $46.0795   $46.08   $46.10   $46.10  
  Purchase #7 $33.52   6.474%   $35.6901   $35.69   $35.70   $35.70  
  7 purchase totals = $895.89       $967.9779   $967.99   $968.00   $968.10