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	$90.98	9.460%	$99.5867	$99.59	$99.60	$99.60
Purchase #2	$37.72	9.457%	$41.2872	$41.29	$41.30	$41.30
Purchase #3	$67.60	8.561%	$73.3872	$73.39	$73.40	$73.40
Purchase #4	$184.73	5.781%	$195.4092	$195.41	$195.40	$195.40
Purchase #5	$249.73	11.206%	$277.7147	$277.71	$277.70	$277.70
Purchase #6	$156.43	3.757%	$162.3071	$162.31	$162.30	$162.30
Purchase #7	$139.70	9.379%	$152.8025	$152.80	$152.80	$152.80
7 purchase totals =	$926.89		$1,002.4946	$1,002.50	$1,002.50	$1,002.50