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	$107.73	4.452%	$112.5261	$112.53	$112.55	$112.50
Purchase #2	$81.61	11.683%	$91.1445	$91.14	$91.15	$91.10
Purchase #3	$214.95	13.191%	$243.3041	$243.30	$243.30	$243.30
Purchase #4	$86.63	5.648%	$91.5229	$91.52	$91.50	$91.50
Purchase #5	$133.90	13.585%	$152.0903	$152.09	$152.10	$152.10
Purchase #6	$82.52	6.112%	$87.5636	$87.56	$87.55	$87.60
Purchase #7	$96.93	4.556%	$101.3461	$101.35	$101.35	$101.30
7 purchase totals =	$804.27		$879.4976	$879.49	$879.50	$879.40