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 $25.77   12.561%   $29.007   $29.01   $29.00   $29.00  
  Purchase #2 $187.32   11.719%   $209.272   $209.27   $209.25   $209.30  
  Purchase #3 $38.41   4.761%   $40.2387   $40.24   $40.25   $40.20  
  Purchase #4 $190.99   10.588%   $211.212   $211.21   $211.20   $211.20  
  Purchase #5 $158.99   13.587%   $180.592   $180.59   $180.60   $180.60  
  Purchase #6 $165.46   12.554%   $186.2318   $186.23   $186.25   $186.20  
  Purchase #7 $132.30   12.142%   $148.3639   $148.36   $148.35   $148.40  
  7 purchase totals = $899.24       $1,004.9174   $1,004.91   $1,004.90   $1,004.90