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	$6.93	3.235%	$7.1542	$7.15	$7.15	$7.20
Purchase #2	$40.66	5.328%	$42.8264	$42.83	$42.85	$42.80
Purchase #3	$154.27	11.548%	$172.0851	$172.09	$172.10	$172.10
Purchase #4	$243.98	10.833%	$270.4104	$270.41	$270.40	$270.40
Purchase #5	$83.33	10.335%	$91.9422	$91.94	$91.95	$91.90
Purchase #6	$154.79	12.568%	$174.244	$174.24	$174.25	$174.20
Purchase #7	$116.40	5.850%	$123.2094	$123.21	$123.20	$123.20
7 purchase totals =	$800.36		$881.8717	$881.87	$881.90	$881.80