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 $151.65   10.679%   $167.8447   $167.84   $167.85   $167.80  
  Purchase #2 $142.93   6.773%   $152.6106   $152.61   $152.60   $152.60  
  Purchase #3 $46.26   3.167%   $47.7251   $47.73   $47.75   $47.70  
  Purchase #4 $22.44   11.509%   $25.0226   $25.02   $25.00   $25.00  
  Purchase #5 $207.34   9.651%   $227.3504   $227.35   $227.35   $227.40  
  Purchase #6 $50.94   6.616%   $54.3102   $54.31   $54.30   $54.30  
  Purchase #7 $89.42   7.670%   $96.2785   $96.28   $96.30   $96.30  
  7 purchase totals = $710.98       $771.1421   $771.14   $771.15   $771.10