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	$19.80	4.212%	$20.634	$20.63	$20.65	$20.60
Purchase #2	$167.48	11.781%	$187.2108	$187.21	$187.20	$187.20
Purchase #3	$238.28	4.635%	$249.3243	$249.32	$249.30	$249.30
Purchase #4	$229.54	6.841%	$245.2428	$245.24	$245.25	$245.20
Purchase #5	$82.52	9.459%	$90.3256	$90.33	$90.35	$90.30
Purchase #6	$59.84	12.123%	$67.0944	$67.09	$67.10	$67.10
Purchase #7	$62.30	10.206%	$68.6583	$68.66	$68.65	$68.70
7 purchase totals =	$859.76		$928.4902	$928.48	$928.50	$928.40