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 $105.65   9.811%   $116.0153   $116.02   $116.00   $116.00  
  Purchase #2 $213.57   11.422%   $237.964   $237.96   $237.95   $238.00  
  Purchase #3 $139.69   9.844%   $153.4411   $153.44   $153.45   $153.40  
  Purchase #4 $233.54   10.462%   $257.973   $257.97   $257.95   $258.00  
  Purchase #5 $109.44   4.753%   $114.6417   $114.64   $114.65   $114.60  
  Purchase #6 $157.77   7.697%   $169.9136   $169.91   $169.90   $169.90  
  Purchase #7 $36.69   9.746%   $40.2658   $40.27   $40.25   $40.30  
  7 purchase totals = $996.35       $1,090.2145   $1,090.21   $1,090.15   $1,090.20