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 $24.27   8.445%   $26.3196   $26.32   $26.30   $26.30  
  Purchase #2 $153.33   4.334%   $159.9753   $159.98   $160.00   $160.00  
  Purchase #3 $82.76   4.737%   $86.6803   $86.68   $86.70   $86.70  
  Purchase #4 $200.61   11.856%   $224.3943   $224.39   $224.40   $224.40  
  Purchase #5 $230.34   6.478%   $245.2614   $245.26   $245.25   $245.30  
  Purchase #6 $246.49   5.370%   $259.7265   $259.73   $259.75   $259.70  
  Purchase #7 $136.39   13.822%   $155.2418   $155.24   $155.25   $155.20  
  7 purchase totals = $1,074.19       $1,157.5992   $1,157.60   $1,157.65   $1,157.60