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	$180.46	13.313%	$204.4846	$204.48	$204.50	$204.50
Purchase #2	$45.65	11.481%	$50.8911	$50.89	$50.90	$50.90
Purchase #3	$130.53	11.182%	$145.1259	$145.13	$145.15	$145.10
Purchase #4	$190.84	9.816%	$209.5729	$209.57	$209.55	$209.60
Purchase #5	$236.33	5.520%	$249.3754	$249.38	$249.40	$249.40
Purchase #6	$170.82	8.612%	$185.531	$185.53	$185.55	$185.50
Purchase #7	$250.47	5.108%	$263.264	$263.26	$263.25	$263.30
7 purchase totals =	$1,205.10		$1,308.2449	$1,308.24	$1,308.30	$1,308.30