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 $171.52   8.274%   $185.7116   $185.71   $185.70   $185.70  
  Purchase #2 $11.88   7.620%   $12.7853   $12.79   $12.80   $12.80  
  Purchase #3 $79.88   13.521%   $90.6806   $90.68   $90.70   $90.70  
  Purchase #4 $242.98   9.446%   $265.9319   $265.93   $265.95   $265.90  
  Purchase #5 $124.76   3.778%   $129.4734   $129.47   $129.45   $129.50  
  Purchase #6 $110.90   11.149%   $123.2642   $123.26   $123.25   $123.30  
  Purchase #7 $192.77   3.859%   $200.209   $200.21   $200.20   $200.20  
  7 purchase totals = $934.69       $1,008.0560   $1,008.05   $1,008.05   $1,008.10