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	$52.84	8.482%	$57.3219	$57.32	$57.30	$57.30
Purchase #2	$202.28	9.239%	$220.9686	$220.97	$220.95	$221.00
Purchase #3	$126.81	11.256%	$141.0837	$141.08	$141.10	$141.10
Purchase #4	$84.31	8.530%	$91.5016	$91.50	$91.50	$91.50
Purchase #5	$91.93	8.112%	$99.3874	$99.39	$99.40	$99.40
Purchase #6	$78.61	13.347%	$89.1021	$89.10	$89.10	$89.10
Purchase #7	$122.68	7.148%	$131.4492	$131.45	$131.45	$131.40
7 purchase totals =	$759.46		$830.8145	$830.81	$830.80	$830.80