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	$6.93	3.769%	$7.1912	$7.19	$7.20	$7.20
Purchase #2	$78.82	6.275%	$83.766	$83.77	$83.75	$83.80
Purchase #3	$103.78	13.544%	$117.836	$117.84	$117.85	$117.80
Purchase #4	$162.72	6.141%	$172.7126	$172.71	$172.70	$172.70
Purchase #5	$130.53	7.843%	$140.7675	$140.77	$140.75	$140.80
Purchase #6	$187.73	6.599%	$200.1183	$200.12	$200.10	$200.10
Purchase #7	$159.40	9.630%	$174.7502	$174.75	$174.75	$174.80
7 purchase totals =	$829.91		$897.1418	$897.15	$897.10	$897.20