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	$78.81	3.147%	$81.2902	$81.29	$81.30	$81.30
Purchase #2	$95.71	5.747%	$101.2105	$101.21	$101.20	$101.20
Purchase #3	$179.71	9.596%	$196.955	$196.96	$196.95	$197.00
Purchase #4	$76.89	11.232%	$85.5263	$85.53	$85.55	$85.50
Purchase #5	$26.91	10.293%	$29.6798	$29.68	$29.70	$29.70
Purchase #6	$39.67	4.356%	$41.398	$41.40	$41.40	$41.40
Purchase #7	$54.64	9.598%	$59.8843	$59.88	$59.90	$59.90
7 purchase totals =	$552.34		$595.9441	$595.95	$596.00	$596.00