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	$67.84	3.818%	$70.4301	$70.43	$70.45	$70.40
Purchase #2	$145.33	10.606%	$160.7437	$160.74	$160.75	$160.70
Purchase #3	$46.89	7.796%	$50.5455	$50.55	$50.55	$50.50
Purchase #4	$161.53	4.647%	$169.0363	$169.04	$169.05	$169.00
Purchase #5	$113.75	9.789%	$124.885	$124.89	$124.90	$124.90
Purchase #6	$54.92	8.322%	$59.4904	$59.49	$59.50	$59.50
Purchase #7	$52.51	11.319%	$58.4536	$58.45	$58.45	$58.50
7 purchase totals =	$642.77		$693.5846	$693.59	$693.65	$693.50