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 $110.69   12.213%   $124.2086   $124.21   $124.20   $124.20  
  Purchase #2 $24.43   9.592%   $26.7733   $26.77   $26.75   $26.80  
  Purchase #3 $164.69   3.513%   $170.4756   $170.48   $170.50   $170.50  
  Purchase #4 $243.80   4.826%   $255.5658   $255.57   $255.55   $255.60  
  Purchase #5 $169.97   13.317%   $192.6049   $192.60   $192.60   $192.60  
  Purchase #6 $81.71   5.227%   $85.981   $85.98   $86.00   $86.00  
  Purchase #7 $196.33   8.325%   $212.6745   $212.67   $212.65   $212.70  
  7 purchase totals = $991.62       $1,068.2837   $1,068.28   $1,068.25   $1,068.40