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 $23.64   12.348%   $26.5591   $26.56   $26.55   $26.60  
  Purchase #2 $214.85   8.582%   $233.2884   $233.29   $233.30   $233.30  
  Purchase #3 $143.75   7.184%   $154.077   $154.08   $154.10   $154.10  
  Purchase #4 $24.56   10.846%   $27.2238   $27.22   $27.20   $27.20  
  Purchase #5 $240.33   8.575%   $260.9383   $260.94   $260.95   $260.90  
  Purchase #6 $72.47   12.555%   $81.5686   $81.57   $81.55   $81.60  
  Purchase #7 $160.55   6.228%   $170.5491   $170.55   $170.55   $170.50  
  7 purchase totals = $880.15       $954.2043   $954.21   $954.20   $954.20