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	$149.27	3.582%	$154.6169	$154.62	$154.60	$154.60
Purchase #2	$42.56	8.300%	$46.0925	$46.09	$46.10	$46.10
Purchase #3	$67.75	10.565%	$74.9078	$74.91	$74.90	$74.90
Purchase #4	$182.95	3.534%	$189.4155	$189.42	$189.40	$189.40
Purchase #5	$232.32	9.382%	$254.1163	$254.12	$254.10	$254.10
Purchase #6	$127.98	9.279%	$139.8553	$139.86	$139.85	$139.90
Purchase #7	$128.36	12.871%	$144.8812	$144.88	$144.90	$144.90
7 purchase totals =	$931.19		$1,003.8855	$1,003.90	$1,003.85	$1,003.90