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 $204.69   8.817%   $222.7375   $222.74   $222.75   $222.70  
  Purchase #2 $142.44   9.352%   $155.761   $155.76   $155.75   $155.80  
  Purchase #3 $51.71   11.830%   $57.8273   $57.83   $57.85   $57.80  
  Purchase #4 $184.35   12.134%   $206.719   $206.72   $206.70   $206.70  
  Purchase #5 $6.64   7.810%   $7.1586   $7.16   $7.15   $7.20  
  Purchase #6 $185.58   7.481%   $199.4632   $199.46   $199.45   $199.50  
  Purchase #7 $188.56   8.678%   $204.9232   $204.92   $204.90   $204.90  
  7 purchase totals = $963.97       $1,054.5898   $1,054.59   $1,054.55   $1,054.60