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	$240.34	10.170%	$264.7826	$264.78	$264.80	$264.80
Purchase #2	$28.53	9.323%	$31.1899	$31.19	$31.20	$31.20
Purchase #3	$91.93	6.482%	$97.8889	$97.89	$97.90	$97.90
Purchase #4	$56.47	7.284%	$60.5833	$60.58	$60.60	$60.60
Purchase #5	$135.85	4.369%	$141.7853	$141.79	$141.80	$141.80
Purchase #6	$86.31	3.829%	$89.6148	$89.61	$89.60	$89.60
Purchase #7	$237.33	3.159%	$244.8273	$244.83	$244.85	$244.80
7 purchase totals =	$876.76		$930.6721	$930.67	$930.75	$930.70