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	$215.31	11.108%	$239.2266	$239.23	$239.25	$239.20
Purchase #2	$31.95	7.392%	$34.3117	$34.31	$34.30	$34.30
Purchase #3	$149.34	12.135%	$167.4624	$167.46	$167.45	$167.50
Purchase #4	$25.46	11.179%	$28.3062	$28.31	$28.30	$28.30
Purchase #5	$94.60	3.148%	$97.578	$97.58	$97.60	$97.60
Purchase #6	$196.48	10.571%	$217.2499	$217.25	$217.25	$217.20
Purchase #7	$33.76	10.612%	$37.3426	$37.34	$37.35	$37.30
7 purchase totals =	$746.90		$821.4774	$821.48	$821.50	$821.40