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	$111.67	9.155%	$121.8934	$121.89	$121.90	$121.90
Purchase #2	$89.91	10.796%	$99.6167	$99.62	$99.60	$99.60
Purchase #3	$57.65	10.197%	$63.5286	$63.53	$63.55	$63.50
Purchase #4	$100.37	4.237%	$104.6227	$104.62	$104.60	$104.60
Purchase #5	$213.81	8.266%	$231.4835	$231.48	$231.50	$231.50
Purchase #6	$77.32	11.413%	$86.1445	$86.14	$86.15	$86.10
Purchase #7	$142.38	3.838%	$147.8445	$147.84	$147.85	$147.80
7 purchase totals =	$793.11		$855.1339	$855.12	$855.15	$855.00