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	$46.90	13.280%	$53.1283	$53.13	$53.15	$53.10
Purchase #2	$78.44	11.873%	$87.7532	$87.75	$87.75	$87.80
Purchase #3	$64.54	10.606%	$71.3851	$71.39	$71.40	$71.40
Purchase #4	$153.69	10.140%	$169.2742	$169.27	$169.25	$169.30
Purchase #5	$245.50	8.645%	$266.7235	$266.72	$266.70	$266.70
Purchase #6	$90.92	8.705%	$98.8346	$98.83	$98.85	$98.80
Purchase #7	$81.54	6.770%	$87.0603	$87.06	$87.05	$87.10
7 purchase totals =	$761.53		$834.1592	$834.15	$834.15	$834.20