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	$137.33	12.179%	$154.0554	$154.06	$154.05	$154.10
Purchase #2	$7.36	11.185%	$8.1832	$8.18	$8.20	$8.20
Purchase #3	$245.94	12.292%	$276.1709	$276.17	$276.15	$276.20
Purchase #4	$196.94	12.797%	$222.1424	$222.14	$222.15	$222.10
Purchase #5	$240.45	5.869%	$254.562	$254.56	$254.55	$254.60
Purchase #6	$209.67	9.623%	$229.8465	$229.85	$229.85	$229.80
Purchase #7	$81.26	11.388%	$90.5139	$90.51	$90.50	$90.50
7 purchase totals =	$1,118.95		$1,235.4743	$1,235.47	$1,235.45	$1,235.50