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 $135.88   11.873%   $152.013   $152.01   $152.00   $152.00  
  Purchase #2 $42.28   10.780%   $46.8378   $46.84   $46.85   $46.80  
  Purchase #3 $77.55   4.542%   $81.0723   $81.07   $81.05   $81.10  
  Purchase #4 $84.69   9.644%   $92.8575   $92.86   $92.85   $92.90  
  Purchase #5 $132.26   5.658%   $139.7433   $139.74   $139.75   $139.70  
  Purchase #6 $223.35   3.563%   $231.308   $231.31   $231.30   $231.30  
  Purchase #7 $51.94   11.522%   $57.9245   $57.92   $57.90   $57.90  
  7 purchase totals = $747.95       $801.7564   $801.75   $801.70   $801.70