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	$12.96	9.436%	$14.1829	$14.18	$14.20	$14.20
Purchase #2	$184.72	8.475%	$200.375	$200.38	$200.40	$200.40
Purchase #3	$239.74	8.165%	$259.3148	$259.31	$259.30	$259.30
Purchase #4	$235.32	12.527%	$264.7985	$264.80	$264.80	$264.80
Purchase #5	$7.25	9.193%	$7.9165	$7.92	$7.90	$7.90
Purchase #6	$80.50	12.834%	$90.8314	$90.83	$90.85	$90.80
Purchase #7	$118.89	9.535%	$130.2262	$130.23	$130.25	$130.20
7 purchase totals =	$879.38		$967.6453	$967.65	$967.70	$967.60