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	$77.33	3.859%	$80.3142	$80.31	$80.30	$80.30
Purchase #2	$128.87	8.503%	$139.8278	$139.83	$139.85	$139.80
Purchase #3	$89.71	12.400%	$100.834	$100.83	$100.85	$100.80
Purchase #4	$230.91	8.315%	$250.1102	$250.11	$250.10	$250.10
Purchase #5	$91.87	11.333%	$102.2816	$102.28	$102.30	$102.30
Purchase #6	$153.30	5.108%	$161.1306	$161.13	$161.15	$161.10
Purchase #7	$171.70	9.861%	$188.6313	$188.63	$188.65	$188.60
7 purchase totals =	$943.69		$1,023.1297	$1,023.12	$1,023.20	$1,023.00