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	$144.85	4.801%	$151.8042	$151.80	$151.80	$151.80
Purchase #2	$164.72	12.844%	$185.8766	$185.88	$185.90	$185.90
Purchase #3	$63.76	9.555%	$69.8523	$69.85	$69.85	$69.90
Purchase #4	$74.61	5.751%	$78.9008	$78.90	$78.90	$78.90
Purchase #5	$67.73	5.413%	$71.3962	$71.40	$71.40	$71.40
Purchase #6	$140.63	13.578%	$159.7247	$159.72	$159.70	$159.70
Purchase #7	$122.36	13.797%	$139.242	$139.24	$139.25	$139.20
7 purchase totals =	$778.66		$856.7968	$856.79	$856.80	$856.80