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 $61.59   6.738%   $65.7399   $65.74   $65.75   $65.70  
  Purchase #2 $218.96   3.451%   $226.5163   $226.52   $226.50   $226.50  
  Purchase #3 $114.83   3.488%   $118.8353   $118.84   $118.85   $118.80  
  Purchase #4 $147.66   3.607%   $152.9861   $152.99   $153.00   $153.00  
  Purchase #5 $129.90   10.349%   $143.3434   $143.34   $143.35   $143.30  
  Purchase #6 $41.71   6.852%   $44.568   $44.57   $44.55   $44.60  
  Purchase #7 $234.44   5.538%   $247.4233   $247.42   $247.40   $247.40  
  7 purchase totals = $949.09       $999.4123   $999.42   $999.40   $999.30