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	$73.61	5.638%	$77.7601	$77.76	$77.75	$77.80
Purchase #2	$41.67	4.449%	$43.5239	$43.52	$43.50	$43.50
Purchase #3	$85.99	8.579%	$93.3671	$93.37	$93.35	$93.40
Purchase #4	$150.55	10.853%	$166.8892	$166.89	$166.90	$166.90
Purchase #5	$106.41	11.216%	$118.3449	$118.34	$118.35	$118.30
Purchase #6	$89.25	8.569%	$96.8978	$96.90	$96.90	$96.90
Purchase #7	$174.95	4.250%	$182.3854	$182.39	$182.40	$182.40
7 purchase totals =	$722.43		$779.1684	$779.17	$779.15	$779.20