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	$198.31	12.850%	$223.7928	$223.79	$223.80	$223.80
Purchase #2	$81.96	8.656%	$89.0545	$89.05	$89.05	$89.10
Purchase #3	$19.92	10.810%	$22.0734	$22.07	$22.05	$22.10
Purchase #4	$127.66	4.430%	$133.3153	$133.32	$133.30	$133.30
Purchase #5	$148.77	7.577%	$160.0423	$160.04	$160.05	$160.00
Purchase #6	$203.37	9.601%	$222.8956	$222.90	$222.90	$222.90
Purchase #7	$79.81	11.651%	$89.1087	$89.11	$89.10	$89.10
7 purchase totals =	$859.80		$940.2826	$940.28	$940.25	$940.30