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	$148.69	3.106%	$153.3083	$153.31	$153.30	$153.30
Purchase #2	$99.88	3.224%	$103.1001	$103.10	$103.10	$103.10
Purchase #3	$52.73	7.549%	$56.7106	$56.71	$56.70	$56.70
Purchase #4	$52.56	5.520%	$55.4613	$55.46	$55.45	$55.50
Purchase #5	$168.62	13.221%	$190.9133	$190.91	$190.90	$190.90
Purchase #6	$128.31	5.350%	$135.1746	$135.17	$135.15	$135.20
Purchase #7	$142.26	10.224%	$156.8047	$156.80	$156.80	$156.80
7 purchase totals =	$793.05		$851.4729	$851.46	$851.40	$851.50