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	$212.58	9.376%	$232.5115	$232.51	$232.50	$232.50
Purchase #2	$178.29	12.199%	$200.0396	$200.04	$200.05	$200.00
Purchase #3	$237.46	5.686%	$250.962	$250.96	$250.95	$251.00
Purchase #4	$85.25	5.351%	$89.8117	$89.81	$89.80	$89.80
Purchase #5	$11.99	7.374%	$12.8741	$12.87	$12.85	$12.90
Purchase #6	$80.72	11.792%	$90.2385	$90.24	$90.25	$90.20
Purchase #7	$190.40	12.829%	$214.8264	$214.83	$214.85	$214.80
7 purchase totals =	$996.69		$1,091.2638	$1,091.26	$1,091.25	$1,091.20