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	$69.33	3.724%	$71.9118	$71.91	$71.90	$71.90
Purchase #2	$227.55	5.727%	$240.5818	$240.58	$240.60	$240.60
Purchase #3	$27.99	6.672%	$29.8575	$29.86	$29.85	$29.90
Purchase #4	$159.72	5.704%	$168.8304	$168.83	$168.85	$168.80
Purchase #5	$26.34	13.353%	$29.8572	$29.86	$29.85	$29.90
Purchase #6	$152.36	12.127%	$170.8367	$170.84	$170.85	$170.80
Purchase #7	$79.46	12.281%	$89.2185	$89.22	$89.20	$89.20
7 purchase totals =	$742.75		$801.0939	$801.10	$801.10	$801.10