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 $111.29   6.232%   $118.2256   $118.23   $118.25   $118.20  
  Purchase #2 $241.44   11.517%   $269.2466   $269.25   $269.25   $269.20  
  Purchase #3 $66.38   12.273%   $74.5268   $74.53   $74.55   $74.50  
  Purchase #4 $250.58   5.487%   $264.3293   $264.33   $264.35   $264.30  
  Purchase #5 $13.48   8.292%   $14.5978   $14.60   $14.60   $14.60  
  Purchase #6 $56.72   3.446%   $58.6746   $58.67   $58.65   $58.70  
  Purchase #7 $223.75   5.856%   $236.8528   $236.85   $236.85   $236.90  
  7 purchase totals = $963.64       $1,036.4535   $1,036.46   $1,036.50   $1,036.40