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	$117.53	3.218%	$121.3121	$121.31	$121.30	$121.30
Purchase #2	$154.76	4.800%	$162.1885	$162.19	$162.20	$162.20
Purchase #3	$106.66	8.185%	$115.3901	$115.39	$115.40	$115.40
Purchase #4	$83.57	7.633%	$89.9489	$89.95	$89.95	$89.90
Purchase #5	$250.51	3.298%	$258.7718	$258.77	$258.75	$258.80
Purchase #6	$64.25	4.790%	$67.3276	$67.33	$67.35	$67.30
Purchase #7	$57.50	13.530%	$65.2798	$65.28	$65.30	$65.30
7 purchase totals =	$834.78		$880.2188	$880.22	$880.25	$880.20