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 $169.92   9.615%   $186.2578   $186.26   $186.25   $186.30  
  Purchase #2 $97.41   13.267%   $110.3334   $110.33   $110.35   $110.30  
  Purchase #3 $122.85   9.207%   $134.1608   $134.16   $134.15   $134.20  
  Purchase #4 $233.73   13.838%   $266.0736   $266.07   $266.05   $266.10  
  Purchase #5 $242.72   5.573%   $256.2468   $256.25   $256.25   $256.20  
  Purchase #6 $204.62   5.849%   $216.5882   $216.59   $216.60   $216.60  
  Purchase #7 $205.45   9.643%   $225.2615   $225.26   $225.25   $225.30  
  7 purchase totals = $1,276.70       $1,394.9221   $1,394.92   $1,394.90   $1,395.00