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 $195.27   4.103%   $203.2819   $203.28   $203.30   $203.30  
  Purchase #2 $78.41   11.172%   $87.17   $87.17   $87.15   $87.20  
  Purchase #3 $86.88   7.155%   $93.0963   $93.10   $93.10   $93.10  
  Purchase #4 $48.42   12.351%   $54.4004   $54.40   $54.40   $54.40  
  Purchase #5 $230.38   13.339%   $261.1104   $261.11   $261.10   $261.10  
  Purchase #6 $127.28   3.702%   $131.9919   $131.99   $132.00   $132.00  
  Purchase #7 $213.53   7.813%   $230.2131   $230.21   $230.20   $230.20  
  7 purchase totals = $980.17       $1,061.2640   $1,061.26   $1,061.25   $1,061.30