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	$35.69	7.403%	$38.3321	$38.33	$38.35	$38.30
Purchase #2	$167.63	10.296%	$184.8892	$184.89	$184.90	$184.90
Purchase #3	$246.95	11.596%	$275.5863	$275.59	$275.60	$275.60
Purchase #4	$106.31	8.114%	$114.936	$114.94	$114.95	$114.90
Purchase #5	$39.99	13.336%	$45.3231	$45.32	$45.30	$45.30
Purchase #6	$87.64	6.386%	$93.2367	$93.24	$93.25	$93.20
Purchase #7	$79.57	4.717%	$83.3233	$83.32	$83.30	$83.30
7 purchase totals =	$763.78		$835.6267	$835.63	$835.65	$835.50