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 $202.44   8.808%   $220.2709   $220.27   $220.25   $220.30  
  Purchase #2 $171.48   8.771%   $186.5205   $186.52   $186.50   $186.50  
  Purchase #3 $55.93   13.837%   $63.669   $63.67   $63.65   $63.70  
  Purchase #4 $9.75   10.500%   $10.7738   $10.77   $10.75   $10.80  
  Purchase #5 $214.83   12.279%   $241.209   $241.21   $241.20   $241.20  
  Purchase #6 $88.41   12.669%   $99.6107   $99.61   $99.60   $99.60  
  Purchase #7 $222.30   6.548%   $236.8562   $236.86   $236.85   $236.90  
  7 purchase totals = $965.14       $1,058.9101   $1,058.91   $1,058.80   $1,059.00