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	$88.80	13.540%	$100.8235	$100.82	$100.80	$100.80
Purchase #2	$153.83	9.683%	$168.7254	$168.73	$168.75	$168.70
Purchase #3	$50.31	6.417%	$53.5384	$53.54	$53.55	$53.50
Purchase #4	$88.54	7.793%	$95.4399	$95.44	$95.45	$95.40
Purchase #5	$31.56	7.592%	$33.956	$33.96	$33.95	$34.00
Purchase #6	$196.56	3.864%	$204.1551	$204.16	$204.15	$204.20
Purchase #7	$147.67	13.708%	$167.9126	$167.91	$167.90	$167.90
7 purchase totals =	$757.27		$824.5509	$824.56	$824.55	$824.50