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	$137.99	9.328%	$150.8617	$150.86	$150.85	$150.90
Purchase #2	$74.67	9.540%	$81.7935	$81.79	$81.80	$81.80
Purchase #3	$215.96	12.761%	$243.5187	$243.52	$243.50	$243.50
Purchase #4	$133.81	6.148%	$142.0366	$142.04	$142.05	$142.00
Purchase #5	$204.89	6.692%	$218.6012	$218.60	$218.60	$218.60
Purchase #6	$57.30	7.747%	$61.739	$61.74	$61.75	$61.70
Purchase #7	$30.75	9.152%	$33.5642	$33.56	$33.55	$33.60
7 purchase totals =	$855.37		$932.1149	$932.11	$932.10	$932.10