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	$92.80	8.482%	$100.6713	$100.67	$100.65	$100.70
Purchase #2	$138.89	12.502%	$156.254	$156.25	$156.25	$156.30
Purchase #3	$64.64	10.399%	$71.3619	$71.36	$71.35	$71.40
Purchase #4	$150.32	4.629%	$157.2783	$157.28	$157.30	$157.30
Purchase #5	$73.45	4.529%	$76.7766	$76.78	$76.80	$76.80
Purchase #6	$211.86	9.114%	$231.1689	$231.17	$231.15	$231.20
Purchase #7	$121.38	8.269%	$131.4169	$131.42	$131.40	$131.40
7 purchase totals =	$853.34		$924.9279	$924.93	$924.90	$925.10