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	$239.95	6.204%	$254.8365	$254.84	$254.85	$254.80
Purchase #2	$136.89	11.215%	$152.2422	$152.24	$152.25	$152.20
Purchase #3	$72.34	7.449%	$77.7286	$77.73	$77.75	$77.70
Purchase #4	$119.83	6.704%	$127.8634	$127.86	$127.85	$127.90
Purchase #5	$37.97	10.118%	$41.8118	$41.81	$41.80	$41.80
Purchase #6	$68.75	13.102%	$77.7576	$77.76	$77.75	$77.80
Purchase #7	$31.71	5.112%	$33.331	$33.33	$33.35	$33.30
7 purchase totals =	$707.44		$765.5711	$765.57	$765.60	$765.50