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	$151.82	3.109%	$156.5401	$156.54	$156.55	$156.50
Purchase #2	$54.60	9.871%	$59.9896	$59.99	$60.00	$60.00
Purchase #3	$234.63	4.424%	$245.01	$245.01	$245.00	$245.00
Purchase #4	$109.85	4.484%	$114.7757	$114.78	$114.80	$114.80
Purchase #5	$35.66	12.600%	$40.1532	$40.15	$40.15	$40.20
Purchase #6	$162.30	11.637%	$181.1869	$181.19	$181.20	$181.20
Purchase #7	$79.92	13.200%	$90.4694	$90.47	$90.45	$90.50
7 purchase totals =	$828.78		$888.1249	$888.13	$888.15	$888.20