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 $23.79   13.182%   $26.926   $26.93   $26.95   $26.90  
  Purchase #2 $158.92   7.590%   $170.982   $170.98   $171.00   $171.00  
  Purchase #3 $156.88   7.631%   $168.8515   $168.85   $168.85   $168.90  
  Purchase #4 $241.26   9.163%   $263.3667   $263.37   $263.35   $263.40  
  Purchase #5 $214.26   3.543%   $221.8512   $221.85   $221.85   $221.90  
  Purchase #6 $71.60   9.341%   $78.2882   $78.29   $78.30   $78.30  
  Purchase #7 $216.50   7.147%   $231.9733   $231.97   $231.95   $232.00  
  7 purchase totals = $1,083.21       $1,162.2389   $1,162.24   $1,162.25   $1,162.40