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	$118.46	10.850%	$131.3129	$131.31	$131.30	$131.30
Purchase #2	$136.94	5.311%	$144.2129	$144.21	$144.20	$144.20
Purchase #3	$38.58	9.487%	$42.2401	$42.24	$42.25	$42.20
Purchase #4	$71.46	3.259%	$73.7889	$73.79	$73.80	$73.80
Purchase #5	$137.98	13.685%	$156.8626	$156.86	$156.85	$156.90
Purchase #6	$142.30	3.243%	$146.9148	$146.91	$146.90	$146.90
Purchase #7	$100.70	8.275%	$109.0329	$109.03	$109.05	$109.00
7 purchase totals =	$746.42		$804.3651	$804.35	$804.35	$804.30