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	$53.55	10.792%	$59.3291	$59.33	$59.35	$59.30
Purchase #2	$79.67	12.355%	$89.5132	$89.51	$89.50	$89.50
Purchase #3	$110.70	13.173%	$125.2825	$125.28	$125.30	$125.30
Purchase #4	$13.76	7.227%	$14.7544	$14.75	$14.75	$14.80
Purchase #5	$71.89	12.445%	$80.8367	$80.84	$80.85	$80.80
Purchase #6	$40.70	7.220%	$43.6385	$43.64	$43.65	$43.60
Purchase #7	$91.90	5.641%	$97.0841	$97.08	$97.10	$97.10
7 purchase totals =	$462.17		$510.4385	$510.43	$510.50	$510.40