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	$33.91	9.593%	$37.163	$37.16	$37.15	$37.20
Purchase #2	$131.77	8.114%	$142.4618	$142.46	$142.45	$142.50
Purchase #3	$143.54	9.226%	$156.783	$156.78	$156.80	$156.80
Purchase #4	$61.80	13.446%	$70.1096	$70.11	$70.10	$70.10
Purchase #5	$38.84	13.690%	$44.1572	$44.16	$44.15	$44.20
Purchase #6	$65.35	11.474%	$72.8483	$72.85	$72.85	$72.80
Purchase #7	$29.85	11.414%	$33.2571	$33.26	$33.25	$33.30
7 purchase totals =	$505.06		$556.7800	$556.78	$556.75	$556.90