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	$131.83	9.595%	$144.4791	$144.48	$144.50	$144.50
Purchase #2	$249.43	9.386%	$272.8415	$272.84	$272.85	$272.80
Purchase #3	$119.92	9.689%	$131.539	$131.54	$131.55	$131.50
Purchase #4	$172.77	3.219%	$178.3315	$178.33	$178.35	$178.30
Purchase #5	$74.92	12.788%	$84.5008	$84.50	$84.50	$84.50
Purchase #6	$55.54	6.753%	$59.2906	$59.29	$59.30	$59.30
Purchase #7	$248.51	11.387%	$276.8078	$276.81	$276.80	$276.80
7 purchase totals =	$1,052.92		$1,147.7903	$1,147.79	$1,147.85	$1,147.70