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	$32.74	13.396%	$37.1259	$37.13	$37.15	$37.10
Purchase #2	$213.90	3.529%	$221.4485	$221.45	$221.45	$221.40
Purchase #3	$94.95	11.415%	$105.7885	$105.79	$105.80	$105.80
Purchase #4	$146.25	8.256%	$158.3244	$158.32	$158.30	$158.30
Purchase #5	$89.52	3.168%	$92.356	$92.36	$92.35	$92.40
Purchase #6	$106.88	12.135%	$119.8499	$119.85	$119.85	$119.80
Purchase #7	$69.54	13.362%	$78.8319	$78.83	$78.85	$78.80
7 purchase totals =	$753.78		$813.7251	$813.73	$813.75	$813.60