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 $244.39   9.563%   $267.761   $267.76   $267.75   $267.80  
  Purchase #2 $161.27   9.415%   $176.4536   $176.45   $176.45   $176.50  
  Purchase #3 $124.36   11.135%   $138.2075   $138.21   $138.20   $138.20  
  Purchase #4 $189.39   7.612%   $203.8064   $203.81   $203.80   $203.80  
  Purchase #5 $234.83   9.838%   $257.9326   $257.93   $257.95   $257.90  
  Purchase #6 $46.42   10.591%   $51.3363   $51.34   $51.35   $51.30  
  Purchase #7 $16.91   4.561%   $17.6813   $17.68   $17.70   $17.70  
  7 purchase totals = $1,017.57       $1,113.1787   $1,113.18   $1,113.20   $1,113.20