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	$140.89	9.874%	$154.8015	$154.80	$154.80	$154.80
Purchase #2	$138.80	9.558%	$152.0665	$152.07	$152.05	$152.10
Purchase #3	$148.33	7.638%	$159.6594	$159.66	$159.65	$159.70
Purchase #4	$82.90	10.722%	$91.7885	$91.79	$91.80	$91.80
Purchase #5	$185.85	9.317%	$203.1656	$203.17	$203.15	$203.20
Purchase #6	$162.56	5.464%	$171.4423	$171.44	$171.45	$171.40
Purchase #7	$68.77	3.385%	$71.0979	$71.10	$71.10	$71.10
7 purchase totals =	$928.10		$1,004.0217	$1,004.03	$1,004.00	$1,004.10