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	$246.44	7.287%	$264.3981	$264.40	$264.40	$264.40
Purchase #2	$216.74	7.626%	$233.2686	$233.27	$233.25	$233.30
Purchase #3	$127.52	9.691%	$139.878	$139.88	$139.90	$139.90
Purchase #4	$229.79	12.418%	$258.3253	$258.33	$258.35	$258.30
Purchase #5	$86.38	11.653%	$96.4459	$96.45	$96.45	$96.40
Purchase #6	$159.87	12.147%	$179.2894	$179.29	$179.30	$179.30
Purchase #7	$171.65	6.216%	$182.3198	$182.32	$182.30	$182.30
7 purchase totals =	$1,238.39		$1,353.9251	$1,353.94	$1,353.95	$1,353.90