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	$104.88	4.524%	$109.6248	$109.62	$109.60	$109.60
Purchase #2	$48.65	11.382%	$54.1873	$54.19	$54.20	$54.20
Purchase #3	$143.25	4.640%	$149.8968	$149.90	$149.90	$149.90
Purchase #4	$245.27	9.330%	$268.1537	$268.15	$268.15	$268.20
Purchase #5	$35.71	5.241%	$37.5816	$37.58	$37.60	$37.60
Purchase #6	$220.69	13.439%	$250.3485	$250.35	$250.35	$250.30
Purchase #7	$58.46	12.588%	$65.8189	$65.82	$65.80	$65.80
7 purchase totals =	$856.91		$935.6116	$935.61	$935.60	$935.60