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	$171.69	8.469%	$186.2304	$186.23	$186.25	$186.20
Purchase #2	$222.40	10.379%	$245.4829	$245.48	$245.50	$245.50
Purchase #3	$37.90	9.195%	$41.3849	$41.38	$41.40	$41.40
Purchase #4	$191.98	5.218%	$201.9975	$202.00	$202.00	$202.00
Purchase #5	$208.48	7.355%	$223.8137	$223.81	$223.80	$223.80
Purchase #6	$159.91	3.469%	$165.4573	$165.46	$165.45	$165.50
Purchase #7	$62.40	8.235%	$67.5386	$67.54	$67.55	$67.50
7 purchase totals =	$1,054.76		$1,131.9053	$1,131.90	$1,131.95	$1,131.90