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 $206.85   11.221%   $230.0606   $230.06   $230.05   $230.10  
  Purchase #2 $222.52   10.753%   $246.4476   $246.45   $246.45   $246.40  
  Purchase #3 $115.53   6.846%   $123.4392   $123.44   $123.45   $123.40  
  Purchase #4 $206.38   12.129%   $231.4118   $231.41   $231.40   $231.40  
  Purchase #5 $223.69   5.757%   $236.5678   $236.57   $236.55   $236.60  
  Purchase #6 $145.41   13.335%   $164.8004   $164.80   $164.80   $164.80  
  Purchase #7 $176.55   3.234%   $182.2596   $182.26   $182.25   $182.30  
  7 purchase totals = $1,296.93       $1,414.9870   $1,414.99   $1,414.95   $1,415.00