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	$89.70	11.139%	$99.6917	$99.69	$99.70	$99.70
Purchase #2	$91.85	6.582%	$97.8956	$97.90	$97.90	$97.90
Purchase #3	$176.36	11.366%	$196.4051	$196.41	$196.40	$196.40
Purchase #4	$23.96	12.538%	$26.9641	$26.96	$26.95	$27.00
Purchase #5	$50.43	7.313%	$54.1179	$54.12	$54.10	$54.10
Purchase #6	$33.72	13.219%	$38.1774	$38.18	$38.20	$38.20
Purchase #7	$215.36	10.848%	$238.7223	$238.72	$238.70	$238.70
7 purchase totals =	$681.38		$751.9741	$751.98	$751.95	$752.00