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	$65.69	10.524%	$72.6032	$72.60	$72.60	$72.60
Purchase #2	$148.84	12.399%	$167.2947	$167.29	$167.30	$167.30
Purchase #3	$141.46	3.612%	$146.5695	$146.57	$146.55	$146.60
Purchase #4	$96.69	6.743%	$103.2098	$103.21	$103.20	$103.20
Purchase #5	$36.96	3.686%	$38.3223	$38.32	$38.30	$38.30
Purchase #6	$5.30	10.367%	$5.8495	$5.85	$5.85	$5.80
Purchase #7	$18.45	12.196%	$20.7002	$20.70	$20.70	$20.70
7 purchase totals =	$513.39		$554.5492	$554.54	$554.50	$554.50