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	$63.37	12.584%	$71.3445	$71.34	$71.35	$71.30
Purchase #2	$164.92	12.566%	$185.6438	$185.64	$185.65	$185.60
Purchase #3	$222.55	9.292%	$243.2293	$243.23	$243.25	$243.20
Purchase #4	$199.26	12.807%	$224.7792	$224.78	$224.80	$224.80
Purchase #5	$234.27	10.198%	$258.1609	$258.16	$258.15	$258.20
Purchase #6	$35.89	8.289%	$38.8649	$38.86	$38.85	$38.90
Purchase #7	$140.37	3.537%	$145.3349	$145.33	$145.35	$145.30
7 purchase totals =	$1,060.63		$1,167.3575	$1,167.34	$1,167.40	$1,167.30