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 $62.38   4.662%   $65.2882   $65.29   $65.30   $65.30  
  Purchase #2 $76.81   12.751%   $86.604   $86.60   $86.60   $86.60  
  Purchase #3 $241.74   4.493%   $252.6014   $252.60   $252.60   $252.60  
  Purchase #4 $120.42   7.177%   $129.0625   $129.06   $129.05   $129.10  
  Purchase #5 $160.25   12.575%   $180.4014   $180.40   $180.40   $180.40  
  Purchase #6 $206.30   11.638%   $230.3092   $230.31   $230.30   $230.30  
  Purchase #7 $127.86   10.496%   $141.2802   $141.28   $141.30   $141.30  
  7 purchase totals = $995.76       $1,085.5469   $1,085.54   $1,085.55   $1,085.60