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	$48.74	4.454%	$50.9109	$50.91	$50.90	$50.90
Purchase #2	$247.44	7.374%	$265.6862	$265.69	$265.70	$265.70
Purchase #3	$144.58	5.328%	$152.2832	$152.28	$152.30	$152.30
Purchase #4	$54.46	12.239%	$61.1254	$61.13	$61.15	$61.10
Purchase #5	$179.43	5.817%	$189.8674	$189.87	$189.85	$189.90
Purchase #6	$247.66	13.190%	$280.3264	$280.33	$280.35	$280.30
Purchase #7	$58.29	3.112%	$60.104	$60.10	$60.10	$60.10
7 purchase totals =	$980.60		$1,060.3035	$1,060.31	$1,060.35	$1,060.30