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	$80.27	12.274%	$90.1223	$90.12	$90.10	$90.10
Purchase #2	$156.73	5.868%	$165.9269	$165.93	$165.95	$165.90
Purchase #3	$60.30	9.380%	$65.9561	$65.96	$65.95	$66.00
Purchase #4	$107.66	8.403%	$116.7067	$116.71	$116.70	$116.70
Purchase #5	$50.32	6.404%	$53.5425	$53.54	$53.55	$53.50
Purchase #6	$91.32	7.356%	$98.0375	$98.04	$98.05	$98.00
Purchase #7	$206.26	5.167%	$216.9175	$216.92	$216.90	$216.90
7 purchase totals =	$752.86		$807.2095	$807.22	$807.20	$807.10