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	$143.44	12.406%	$161.2352	$161.24	$161.25	$161.20
Purchase #2	$203.56	4.221%	$212.1523	$212.15	$212.15	$212.20
Purchase #3	$227.50	10.126%	$250.5367	$250.54	$250.55	$250.50
Purchase #4	$121.50	4.714%	$127.2275	$127.23	$127.25	$127.20
Purchase #5	$48.90	8.212%	$52.9157	$52.92	$52.90	$52.90
Purchase #6	$27.62	6.165%	$29.3228	$29.32	$29.30	$29.30
Purchase #7	$92.26	7.467%	$99.1491	$99.15	$99.15	$99.10
7 purchase totals =	$864.78		$932.5393	$932.55	$932.55	$932.40