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	$45.28	5.512%	$47.7758	$47.78	$47.80	$47.80
Purchase #2	$95.74	5.652%	$101.1512	$101.15	$101.15	$101.20
Purchase #3	$37.33	12.144%	$41.8634	$41.86	$41.85	$41.90
Purchase #4	$188.75	12.612%	$212.5552	$212.56	$212.55	$212.60
Purchase #5	$227.50	7.193%	$243.8641	$243.86	$243.85	$243.90
Purchase #6	$105.35	5.782%	$111.4413	$111.44	$111.45	$111.40
Purchase #7	$244.75	6.732%	$261.2266	$261.23	$261.25	$261.20
7 purchase totals =	$944.70		$1,019.8776	$1,019.88	$1,019.90	$1,020.00