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	$51.79	6.780%	$55.3014	$55.30	$55.30	$55.30
Purchase #2	$90.73	6.658%	$96.7708	$96.77	$96.75	$96.80
Purchase #3	$40.74	7.700%	$43.877	$43.88	$43.90	$43.90
Purchase #4	$163.87	6.664%	$174.7903	$174.79	$174.80	$174.80
Purchase #5	$217.78	13.605%	$247.409	$247.41	$247.40	$247.40
Purchase #6	$89.37	11.537%	$99.6806	$99.68	$99.70	$99.70
Purchase #7	$190.30	12.162%	$213.4443	$213.44	$213.45	$213.40
7 purchase totals =	$844.58		$931.2734	$931.27	$931.30	$931.30