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 $188.47   13.778%   $214.4374   $214.44   $214.45   $214.40  
  Purchase #2 $24.33   10.531%   $26.8922   $26.89   $26.90   $26.90  
  Purchase #3 $206.82   6.353%   $219.9593   $219.96   $219.95   $220.00  
  Purchase #4 $18.86   10.530%   $20.846   $20.85   $20.85   $20.80  
  Purchase #5 $248.87   8.198%   $269.2724   $269.27   $269.25   $269.30  
  Purchase #6 $243.27   13.651%   $276.4788   $276.48   $276.50   $276.50  
  Purchase #7 $201.64   10.215%   $222.2375   $222.24   $222.25   $222.20  
  7 purchase totals = $1,132.26       $1,250.1236   $1,250.13   $1,250.15   $1,250.10