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 $249.58   10.614%   $276.0704   $276.07   $276.05   $276.10  
  Purchase #2 $14.36   4.558%   $15.0145   $15.01   $15.00   $15.00  
  Purchase #3 $224.48   9.627%   $246.0907   $246.09   $246.10   $246.10  
  Purchase #4 $234.60   12.597%   $264.1526   $264.15   $264.15   $264.20  
  Purchase #5 $24.31   8.297%   $26.327   $26.33   $26.35   $26.30  
  Purchase #6 $154.51   3.624%   $160.1094   $160.11   $160.10   $160.10  
  Purchase #7 $200.51   10.241%   $221.0442   $221.04   $221.05   $221.00  
  7 purchase totals = $1,102.35       $1,208.8088   $1,208.80   $1,208.80   $1,208.80