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	$101.69	5.541%	$107.3246	$107.32	$107.30	$107.30
Purchase #2	$101.98	12.586%	$114.8152	$114.82	$114.80	$114.80
Purchase #3	$143.73	9.155%	$156.8885	$156.89	$156.90	$156.90
Purchase #4	$243.86	10.221%	$268.7849	$268.78	$268.80	$268.80
Purchase #5	$102.46	8.450%	$111.1179	$111.12	$111.10	$111.10
Purchase #6	$198.27	10.651%	$219.3877	$219.39	$219.40	$219.40
Purchase #7	$92.30	12.668%	$103.9926	$103.99	$104.00	$104.00
7 purchase totals =	$984.29		$1,082.3114	$1,082.31	$1,082.30	$1,082.30