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	$133.53	11.181%	$148.46	$148.46	$148.45	$148.50
Purchase #2	$39.76	13.402%	$45.0886	$45.09	$45.10	$45.10
Purchase #3	$110.92	12.627%	$124.9259	$124.93	$124.95	$124.90
Purchase #4	$88.83	6.359%	$94.4787	$94.48	$94.50	$94.50
Purchase #5	$116.99	7.113%	$125.3115	$125.31	$125.30	$125.30
Purchase #6	$28.70	9.460%	$31.415	$31.42	$31.40	$31.40
Purchase #7	$152.44	10.511%	$168.463	$168.46	$168.45	$168.50
7 purchase totals =	$671.17		$738.1427	$738.15	$738.15	$738.20