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	$102.61	6.427%	$109.2047	$109.20	$109.20	$109.20
Purchase #2	$134.68	11.670%	$150.3972	$150.40	$150.40	$150.40
Purchase #3	$52.31	13.373%	$59.3054	$59.31	$59.30	$59.30
Purchase #4	$32.69	3.594%	$33.8649	$33.86	$33.85	$33.90
Purchase #5	$69.29	12.373%	$77.8633	$77.86	$77.85	$77.90
Purchase #6	$79.68	12.651%	$89.7603	$89.76	$89.75	$89.80
Purchase #7	$172.39	11.507%	$192.2269	$192.23	$192.25	$192.20
7 purchase totals =	$643.65		$712.6227	$712.62	$712.60	$712.70