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	$106.30	5.655%	$112.3113	$112.31	$112.30	$112.30
Purchase #2	$116.30	3.574%	$120.4566	$120.46	$120.45	$120.50
Purchase #3	$33.97	9.201%	$37.0956	$37.10	$37.10	$37.10
Purchase #4	$241.72	11.760%	$270.1463	$270.15	$270.15	$270.10
Purchase #5	$75.96	5.742%	$80.3216	$80.32	$80.30	$80.30
Purchase #6	$128.57	10.486%	$142.0519	$142.05	$142.05	$142.10
Purchase #7	$221.30	9.169%	$241.591	$241.59	$241.60	$241.60
7 purchase totals =	$924.12		$1,003.9743	$1,003.98	$1,003.95	$1,004.00