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	$111.55	8.234%	$120.735	$120.74	$120.75	$120.70
Purchase #2	$206.69	13.362%	$234.3079	$234.31	$234.30	$234.30
Purchase #3	$101.90	3.657%	$105.6265	$105.63	$105.65	$105.60
Purchase #4	$56.94	5.263%	$59.9368	$59.94	$59.95	$59.90
Purchase #5	$198.84	10.611%	$219.9389	$219.94	$219.95	$219.90
Purchase #6	$126.44	12.454%	$142.1868	$142.19	$142.20	$142.20
Purchase #7	$128.55	12.242%	$144.2871	$144.29	$144.30	$144.30
7 purchase totals =	$930.91		$1,027.0190	$1,027.04	$1,027.10	$1,026.90