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	$74.27	13.710%	$84.4524	$84.45	$84.45	$84.50
Purchase #2	$56.78	8.731%	$61.7375	$61.74	$61.75	$61.70
Purchase #3	$32.31	3.285%	$33.3714	$33.37	$33.35	$33.40
Purchase #4	$221.53	5.578%	$233.8869	$233.89	$233.90	$233.90
Purchase #5	$170.92	4.800%	$179.1242	$179.12	$179.10	$179.10
Purchase #6	$180.32	3.514%	$186.6564	$186.66	$186.65	$186.70
Purchase #7	$71.67	9.707%	$78.627	$78.63	$78.65	$78.60
7 purchase totals =	$807.80		$857.8558	$857.86	$857.85	$857.90