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 $184.76   8.122%   $199.7662   $199.77   $199.75   $199.80  
  Purchase #2 $179.96   4.870%   $188.7241   $188.72   $188.70   $188.70  
  Purchase #3 $206.79   13.720%   $235.1616   $235.16   $235.15   $235.20  
  Purchase #4 $50.83   8.741%   $55.2731   $55.27   $55.25   $55.30  
  Purchase #5 $250.52   8.648%   $272.185   $272.19   $272.20   $272.20  
  Purchase #6 $13.88   6.261%   $14.749   $14.75   $14.75   $14.70  
  Purchase #7 $49.28   3.812%   $51.1586   $51.16   $51.15   $51.20  
  7 purchase totals = $936.02       $1,017.0176   $1,017.02   $1,016.95   $1,017.10