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	$166.71	9.561%	$182.6491	$182.65	$182.65	$182.60
Purchase #2	$36.51	9.130%	$39.8434	$39.84	$39.85	$39.80
Purchase #3	$83.63	6.503%	$89.0685	$89.07	$89.05	$89.10
Purchase #4	$73.73	9.351%	$80.6245	$80.62	$80.60	$80.60
Purchase #5	$29.76	11.120%	$33.0693	$33.07	$33.05	$33.10
Purchase #6	$46.86	12.171%	$52.5633	$52.56	$52.55	$52.60
Purchase #7	$142.80	5.850%	$151.1538	$151.15	$151.15	$151.20
7 purchase totals =	$580.00		$628.9719	$628.96	$628.90	$629.00