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	$175.74	11.616%	$196.154	$196.15	$196.15	$196.20
Purchase #2	$93.63	10.241%	$103.2186	$103.22	$103.20	$103.20
Purchase #3	$125.26	11.852%	$140.1058	$140.11	$140.10	$140.10
Purchase #4	$45.53	11.148%	$50.6057	$50.61	$50.60	$50.60
Purchase #5	$88.89	8.804%	$96.7159	$96.72	$96.70	$96.70
Purchase #6	$139.39	11.812%	$155.8547	$155.85	$155.85	$155.90
Purchase #7	$89.70	8.682%	$97.4878	$97.49	$97.50	$97.50
7 purchase totals =	$758.14		$840.1425	$840.15	$840.10	$840.20