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	$72.40	9.444%	$79.2375	$79.24	$79.25	$79.20
Purchase #2	$85.88	10.454%	$94.8579	$94.86	$94.85	$94.90
Purchase #3	$82.42	10.560%	$91.1236	$91.12	$91.10	$91.10
Purchase #4	$61.38	7.396%	$65.9197	$65.92	$65.90	$65.90
Purchase #5	$158.61	13.664%	$180.2825	$180.28	$180.30	$180.30
Purchase #6	$36.35	4.562%	$38.0083	$38.01	$38.00	$38.00
Purchase #7	$23.28	9.479%	$25.4867	$25.49	$25.50	$25.50
7 purchase totals =	$520.32		$574.9162	$574.92	$574.90	$574.90