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	$243.92	13.623%	$277.1492	$277.15	$277.15	$277.10
Purchase #2	$11.73	8.761%	$12.7577	$12.76	$12.75	$12.80
Purchase #3	$82.73	3.742%	$85.8258	$85.83	$85.85	$85.80
Purchase #4	$145.81	8.598%	$158.3467	$158.35	$158.35	$158.30
Purchase #5	$132.84	6.501%	$141.4759	$141.48	$141.50	$141.50
Purchase #6	$191.90	7.791%	$206.8509	$206.85	$206.85	$206.90
Purchase #7	$78.51	13.224%	$88.8922	$88.89	$88.90	$88.90
7 purchase totals =	$887.44		$971.2984	$971.31	$971.35	$971.30