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	$231.30	8.149%	$250.1486	$250.15	$250.15	$250.10
Purchase #2	$239.73	12.164%	$268.8908	$268.89	$268.90	$268.90
Purchase #3	$151.63	6.533%	$161.536	$161.54	$161.55	$161.50
Purchase #4	$233.56	9.579%	$255.9327	$255.93	$255.95	$255.90
Purchase #5	$180.68	13.362%	$204.8225	$204.82	$204.80	$204.80
Purchase #6	$59.97	11.814%	$67.0549	$67.05	$67.05	$67.10
Purchase #7	$6.58	7.834%	$7.0955	$7.10	$7.10	$7.10
7 purchase totals =	$1,103.45		$1,215.4810	$1,215.48	$1,215.50	$1,215.40