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	$152.94	5.594%	$161.4955	$161.50	$161.50	$161.50
Purchase #2	$196.84	5.805%	$208.2666	$208.27	$208.25	$208.30
Purchase #3	$207.76	6.427%	$221.1127	$221.11	$221.10	$221.10
Purchase #4	$180.85	8.681%	$196.5496	$196.55	$196.55	$196.50
Purchase #5	$129.98	5.495%	$137.1224	$137.12	$137.10	$137.10
Purchase #6	$198.33	12.844%	$223.8035	$223.80	$223.80	$223.80
Purchase #7	$85.58	11.507%	$95.4277	$95.43	$95.45	$95.40
7 purchase totals =	$1,152.28		$1,243.7780	$1,243.78	$1,243.75	$1,243.70