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	$227.61	12.411%	$255.8587	$255.86	$255.85	$255.90
Purchase #2	$84.44	9.308%	$92.2997	$92.30	$92.30	$92.30
Purchase #3	$123.66	4.445%	$129.1567	$129.16	$129.15	$129.20
Purchase #4	$178.59	12.359%	$200.6619	$200.66	$200.65	$200.70
Purchase #5	$237.76	3.266%	$245.5252	$245.53	$245.55	$245.50
Purchase #6	$92.78	5.740%	$98.1056	$98.11	$98.10	$98.10
Purchase #7	$40.58	11.179%	$45.1164	$45.12	$45.10	$45.10
7 purchase totals =	$985.42		$1,066.7242	$1,066.74	$1,066.70	$1,066.80