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	$10.57	4.290%	$11.0235	$11.02	$11.00	$11.00
Purchase #2	$150.50	6.743%	$160.6482	$160.65	$160.65	$160.60
Purchase #3	$37.61	13.180%	$42.567	$42.57	$42.55	$42.60
Purchase #4	$10.95	5.329%	$11.5335	$11.53	$11.55	$11.50
Purchase #5	$212.36	12.596%	$239.1089	$239.11	$239.10	$239.10
Purchase #6	$123.74	6.551%	$131.8462	$131.85	$131.85	$131.80
Purchase #7	$188.67	12.836%	$212.8877	$212.89	$212.90	$212.90
7 purchase totals =	$734.40		$809.6150	$809.62	$809.60	$809.50