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	$98.76	12.734%	$111.3361	$111.34	$111.35	$111.30
Purchase #2	$56.97	12.275%	$63.9631	$63.96	$63.95	$64.00
Purchase #3	$146.73	12.597%	$165.2136	$165.21	$165.20	$165.20
Purchase #4	$242.86	3.269%	$250.7991	$250.80	$250.80	$250.80
Purchase #5	$88.50	9.484%	$96.8933	$96.89	$96.90	$96.90
Purchase #6	$113.45	12.596%	$127.7402	$127.74	$127.75	$127.70
Purchase #7	$80.39	6.739%	$85.8075	$85.81	$85.80	$85.80
7 purchase totals =	$827.66		$901.7529	$901.75	$901.75	$901.70