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	$176.90	6.550%	$188.487	$188.49	$188.50	$188.50
Purchase #2	$245.77	8.175%	$265.8617	$265.86	$265.85	$265.90
Purchase #3	$59.37	4.227%	$61.8796	$61.88	$61.90	$61.90
Purchase #4	$99.73	11.809%	$111.5071	$111.51	$111.50	$111.50
Purchase #5	$233.33	10.384%	$257.559	$257.56	$257.55	$257.60
Purchase #6	$222.53	7.295%	$238.7636	$238.76	$238.75	$238.80
Purchase #7	$221.33	7.587%	$238.1223	$238.12	$238.10	$238.10
7 purchase totals =	$1,258.96		$1,362.1803	$1,362.18	$1,362.15	$1,362.30