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	$38.75	9.516%	$42.4375	$42.44	$42.45	$42.40
Purchase #2	$102.64	11.217%	$114.1531	$114.15	$114.15	$114.20
Purchase #3	$132.82	7.563%	$142.8652	$142.87	$142.85	$142.90
Purchase #4	$125.68	4.611%	$131.4751	$131.48	$131.50	$131.50
Purchase #5	$194.45	4.667%	$203.525	$203.53	$203.55	$203.50
Purchase #6	$232.63	4.769%	$243.7241	$243.72	$243.70	$243.70
Purchase #7	$68.66	4.241%	$71.5719	$71.57	$71.55	$71.60
7 purchase totals =	$895.63		$949.7519	$949.76	$949.75	$949.80