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	$46.43	11.544%	$51.7899	$51.79	$51.80	$51.80
Purchase #2	$77.32	7.539%	$83.1492	$83.15	$83.15	$83.10
Purchase #3	$218.25	13.781%	$248.327	$248.33	$248.35	$248.30
Purchase #4	$191.64	10.613%	$211.9788	$211.98	$212.00	$212.00
Purchase #5	$54.75	10.623%	$60.5661	$60.57	$60.55	$60.60
Purchase #6	$157.40	6.709%	$167.96	$167.96	$167.95	$168.00
Purchase #7	$166.73	7.113%	$178.5895	$178.59	$178.60	$178.60
7 purchase totals =	$912.52		$1,002.3605	$1,002.37	$1,002.40	$1,002.40