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 $116.57   9.263%   $127.3679   $127.37   $127.35   $127.40  
  Purchase #2 $240.93   13.279%   $272.9231   $272.92   $272.90   $272.90  
  Purchase #3 $163.97   11.858%   $183.4136   $183.41   $183.40   $183.40  
  Purchase #4 $24.31   11.760%   $27.1689   $27.17   $27.15   $27.20  
  Purchase #5 $112.27   10.629%   $124.2032   $124.20   $124.20   $124.20  
  Purchase #6 $64.88   8.466%   $70.3727   $70.37   $70.35   $70.40  
  Purchase #7 $198.72   3.846%   $206.3628   $206.36   $206.35   $206.40  
  7 purchase totals = $921.65       $1,011.8122   $1,011.80   $1,011.70   $1,011.90