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 $215.48   12.273%   $241.9259   $241.93   $241.95   $241.90  
  Purchase #2 $150.79   12.315%   $169.3598   $169.36   $169.35   $169.40  
  Purchase #3 $107.97   3.276%   $111.5071   $111.51   $111.50   $111.50  
  Purchase #4 $60.57   7.495%   $65.1097   $65.11   $65.10   $65.10  
  Purchase #5 $42.96   10.280%   $47.3763   $47.38   $47.40   $47.40  
  Purchase #6 $117.33   10.650%   $129.8256   $129.83   $129.85   $129.80  
  Purchase #7 $242.38   12.601%   $272.9223   $272.92   $272.90   $272.90  
  7 purchase totals = $937.48       $1,038.0267   $1,038.04   $1,038.05   $1,038.00