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	$128.91	9.413%	$141.0443	$141.04	$141.05	$141.00
Purchase #2	$72.84	10.253%	$80.3083	$80.31	$80.30	$80.30
Purchase #3	$238.83	12.452%	$268.5691	$268.57	$268.55	$268.60
Purchase #4	$39.72	6.231%	$42.195	$42.20	$42.20	$42.20
Purchase #5	$151.58	3.283%	$156.5564	$156.56	$156.55	$156.60
Purchase #6	$25.77	11.693%	$28.7833	$28.78	$28.80	$28.80
Purchase #7	$191.78	4.461%	$200.3353	$200.34	$200.35	$200.30
7 purchase totals =	$849.43		$917.7917	$917.80	$917.80	$917.80