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	$65.72	11.850%	$73.5078	$73.51	$73.50	$73.50
Purchase #2	$51.47	9.774%	$56.5007	$56.50	$56.50	$56.50
Purchase #3	$86.41	12.148%	$96.9071	$96.91	$96.90	$96.90
Purchase #4	$199.80	11.519%	$222.815	$222.82	$222.80	$222.80
Purchase #5	$54.72	7.230%	$58.6763	$58.68	$58.70	$58.70
Purchase #6	$82.31	5.619%	$86.935	$86.94	$86.95	$86.90
Purchase #7	$65.56	8.159%	$70.909	$70.91	$70.90	$70.90
7 purchase totals =	$605.99		$666.2509	$666.27	$666.25	$666.20