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	$39.70	7.115%	$42.5247	$42.52	$42.50	$42.50
Purchase #2	$99.77	9.800%	$109.5475	$109.55	$109.55	$109.50
Purchase #3	$159.51	11.600%	$178.0132	$178.01	$178.00	$178.00
Purchase #4	$162.34	4.643%	$169.8774	$169.88	$169.90	$169.90
Purchase #5	$131.62	12.176%	$147.6461	$147.65	$147.65	$147.60
Purchase #6	$12.34	3.539%	$12.7767	$12.78	$12.80	$12.80
Purchase #7	$55.51	6.224%	$58.9649	$58.96	$58.95	$59.00
7 purchase totals =	$660.79		$719.3505	$719.35	$719.35	$719.30