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	$242.95	12.683%	$273.7633	$273.76	$273.75	$273.80
Purchase #2	$147.66	12.596%	$166.2593	$166.26	$166.25	$166.30
Purchase #3	$95.91	5.272%	$100.9664	$100.97	$100.95	$101.00
Purchase #4	$81.26	9.731%	$89.1674	$89.17	$89.15	$89.20
Purchase #5	$89.54	7.513%	$96.2671	$96.27	$96.25	$96.30
Purchase #6	$155.75	12.297%	$174.9026	$174.90	$174.90	$174.90
Purchase #7	$12.76	13.718%	$14.5104	$14.51	$14.50	$14.50
7 purchase totals =	$825.83		$915.8365	$915.84	$915.75	$916.00