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	$84.89	7.337%	$91.1184	$91.12	$91.10	$91.10
Purchase #2	$168.86	3.293%	$174.4206	$174.42	$174.40	$174.40
Purchase #3	$96.63	10.302%	$106.5848	$106.58	$106.60	$106.60
Purchase #4	$27.42	9.196%	$29.9415	$29.94	$29.95	$29.90
Purchase #5	$92.77	9.711%	$101.7789	$101.78	$101.80	$101.80
Purchase #6	$96.98	6.761%	$103.5368	$103.54	$103.55	$103.50
Purchase #7	$152.34	9.729%	$167.1612	$167.16	$167.15	$167.20
7 purchase totals =	$719.89		$774.5422	$774.54	$774.55	$774.50