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	$145.53	10.566%	$160.9067	$160.91	$160.90	$160.90
Purchase #2	$131.64	6.410%	$140.0781	$140.08	$140.10	$140.10
Purchase #3	$84.80	3.639%	$87.8859	$87.89	$87.90	$87.90
Purchase #4	$83.74	9.272%	$91.5044	$91.50	$91.50	$91.50
Purchase #5	$191.40	10.339%	$211.1888	$211.19	$211.20	$211.20
Purchase #6	$246.60	9.180%	$269.2379	$269.24	$269.25	$269.20
Purchase #7	$71.69	9.223%	$78.302	$78.30	$78.30	$78.30
7 purchase totals =	$955.40		$1,039.1038	$1,039.11	$1,039.15	$1,039.10