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	$73.59	6.179%	$78.1371	$78.14	$78.15	$78.10
Purchase #2	$228.86	9.442%	$250.469	$250.47	$250.45	$250.50
Purchase #3	$154.60	13.138%	$174.9113	$174.91	$174.90	$174.90
Purchase #4	$67.90	4.330%	$70.8401	$70.84	$70.85	$70.80
Purchase #5	$42.78	9.357%	$46.7829	$46.78	$46.80	$46.80
Purchase #6	$56.91	3.182%	$58.7209	$58.72	$58.70	$58.70
Purchase #7	$99.33	4.616%	$103.9151	$103.92	$103.90	$103.90
7 purchase totals =	$723.97		$783.7764	$783.78	$783.75	$783.70