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	$221.54	4.453%	$231.4052	$231.41	$231.40	$231.40
Purchase #2	$96.83	11.872%	$108.3257	$108.33	$108.35	$108.30
Purchase #3	$77.42	3.636%	$80.235	$80.24	$80.25	$80.20
Purchase #4	$78.77	9.560%	$86.3004	$86.30	$86.30	$86.30
Purchase #5	$56.53	8.525%	$61.3492	$61.35	$61.35	$61.30
Purchase #6	$191.88	12.380%	$215.6347	$215.63	$215.65	$215.60
Purchase #7	$18.72	8.531%	$20.317	$20.32	$20.30	$20.30
7 purchase totals =	$741.69		$803.5672	$803.58	$803.60	$803.40