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	$123.45	6.721%	$131.7471	$131.75	$131.75	$131.70
Purchase #2	$185.61	12.280%	$208.4029	$208.40	$208.40	$208.40
Purchase #3	$168.95	9.109%	$184.3397	$184.34	$184.35	$184.30
Purchase #4	$42.47	4.610%	$44.4279	$44.43	$44.45	$44.40
Purchase #5	$119.51	9.181%	$130.4822	$130.48	$130.50	$130.50
Purchase #6	$71.31	3.589%	$73.8693	$73.87	$73.85	$73.90
Purchase #7	$210.44	13.524%	$238.8999	$238.90	$238.90	$238.90
7 purchase totals =	$921.74		$1,012.1690	$1,012.17	$1,012.20	$1,012.10