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	$111.98	6.554%	$119.3192	$119.32	$119.30	$119.30
Purchase #2	$90.77	8.494%	$98.48	$98.48	$98.50	$98.50
Purchase #3	$147.41	8.550%	$160.0136	$160.01	$160.00	$160.00
Purchase #4	$120.30	6.332%	$127.9174	$127.92	$127.90	$127.90
Purchase #5	$250.35	10.166%	$275.8006	$275.80	$275.80	$275.80
Purchase #6	$78.31	10.731%	$86.7134	$86.71	$86.70	$86.70
Purchase #7	$191.81	3.487%	$198.4984	$198.50	$198.50	$198.50
7 purchase totals =	$990.93		$1,066.7426	$1,066.74	$1,066.70	$1,066.70