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	$108.51	11.342%	$120.8172	$120.82	$120.80	$120.80
Purchase #2	$182.81	7.311%	$196.1752	$196.18	$196.20	$196.20
Purchase #3	$82.56	13.313%	$93.5512	$93.55	$93.55	$93.60
Purchase #4	$223.32	7.494%	$240.0556	$240.06	$240.05	$240.10
Purchase #5	$79.83	10.869%	$88.5067	$88.51	$88.50	$88.50
Purchase #6	$191.78	11.222%	$213.3016	$213.30	$213.30	$213.30
Purchase #7	$118.77	11.497%	$132.425	$132.43	$132.45	$132.40
7 purchase totals =	$987.58		$1,084.8325	$1,084.85	$1,084.85	$1,084.90