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	$109.72	12.499%	$123.4339	$123.43	$123.45	$123.40
Purchase #2	$221.58	11.199%	$246.3947	$246.39	$246.40	$246.40
Purchase #3	$240.38	10.465%	$265.5358	$265.54	$265.55	$265.50
Purchase #4	$131.84	10.415%	$145.5711	$145.57	$145.55	$145.60
Purchase #5	$71.32	6.223%	$75.7582	$75.76	$75.75	$75.80
Purchase #6	$146.60	9.655%	$160.7542	$160.75	$160.75	$160.80
Purchase #7	$133.48	13.751%	$151.8348	$151.83	$151.85	$151.80
7 purchase totals =	$1,054.92		$1,169.2827	$1,169.27	$1,169.30	$1,169.30