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 $68.61   11.172%   $76.2751   $76.28   $76.30   $76.30  
  Purchase #2 $181.67   5.164%   $191.0514   $191.05   $191.05   $191.10  
  Purchase #3 $124.29   9.771%   $136.4344   $136.43   $136.45   $136.40  
  Purchase #4 $162.80   10.356%   $179.6596   $179.66   $179.65   $179.70  
  Purchase #5 $214.83   3.439%   $222.218   $222.22   $222.20   $222.20  
  Purchase #6 $41.61   7.605%   $44.7744   $44.77   $44.75   $44.80  
  Purchase #7 $63.42   8.475%   $68.7948   $68.79   $68.80   $68.80  
  7 purchase totals = $857.23       $919.2077   $919.20   $919.20   $919.30