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	$144.56	12.505%	$162.6372	$162.64	$162.65	$162.60
Purchase #2	$168.99	11.430%	$188.3056	$188.31	$188.30	$188.30
Purchase #3	$135.34	6.350%	$143.9341	$143.93	$143.95	$143.90
Purchase #4	$123.45	6.794%	$131.8372	$131.84	$131.85	$131.80
Purchase #5	$52.80	4.737%	$55.3011	$55.30	$55.30	$55.30
Purchase #6	$174.41	12.476%	$196.1694	$196.17	$196.15	$196.20
Purchase #7	$36.40	10.383%	$40.1794	$40.18	$40.20	$40.20
7 purchase totals =	$835.95		$918.3640	$918.37	$918.40	$918.30