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	$245.72	9.861%	$269.9504	$269.95	$269.95	$270.00
Purchase #2	$84.40	12.215%	$94.7095	$94.71	$94.70	$94.70
Purchase #3	$238.46	7.262%	$255.777	$255.78	$255.80	$255.80
Purchase #4	$185.37	3.494%	$191.8468	$191.85	$191.85	$191.80
Purchase #5	$184.88	3.121%	$190.6501	$190.65	$190.65	$190.70
Purchase #6	$80.40	11.116%	$89.3373	$89.34	$89.35	$89.30
Purchase #7	$33.95	3.265%	$35.0585	$35.06	$35.05	$35.10
7 purchase totals =	$1,053.18		$1,127.3296	$1,127.34	$1,127.35	$1,127.40