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	$71.60	9.568%	$78.4507	$78.45	$78.45	$78.50
Purchase #2	$64.30	4.817%	$67.3973	$67.40	$67.40	$67.40
Purchase #3	$100.55	3.556%	$104.1256	$104.13	$104.15	$104.10
Purchase #4	$27.60	13.170%	$31.2349	$31.23	$31.25	$31.20
Purchase #5	$123.80	9.349%	$135.3741	$135.37	$135.35	$135.40
Purchase #6	$58.49	6.258%	$62.1503	$62.15	$62.15	$62.20
Purchase #7	$223.76	11.655%	$249.8392	$249.84	$249.85	$249.80
7 purchase totals =	$670.10		$728.5721	$728.57	$728.60	$728.60