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	$72.91	8.215%	$78.8996	$78.90	$78.90	$78.90
Purchase #2	$76.84	12.521%	$86.4611	$86.46	$86.45	$86.50
Purchase #3	$99.82	9.810%	$109.6123	$109.61	$109.60	$109.60
Purchase #4	$240.46	12.662%	$270.907	$270.91	$270.90	$270.90
Purchase #5	$115.33	12.857%	$130.158	$130.16	$130.15	$130.20
Purchase #6	$50.64	5.750%	$53.5518	$53.55	$53.55	$53.60
Purchase #7	$89.68	7.323%	$96.2473	$96.25	$96.25	$96.20
7 purchase totals =	$745.68		$825.8371	$825.84	$825.80	$825.90