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	$81.83	11.536%	$91.2699	$91.27	$91.25	$91.30
Purchase #2	$210.31	10.294%	$231.9593	$231.96	$231.95	$232.00
Purchase #3	$127.73	9.612%	$140.0074	$140.01	$140.00	$140.00
Purchase #4	$180.30	5.413%	$190.0596	$190.06	$190.05	$190.10
Purchase #5	$54.51	5.608%	$57.5669	$57.57	$57.55	$57.60
Purchase #6	$34.31	9.216%	$37.472	$37.47	$37.45	$37.50
Purchase #7	$219.33	4.822%	$229.9061	$229.91	$229.90	$229.90
7 purchase totals =	$908.32		$978.2412	$978.25	$978.15	$978.40