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	$84.46	7.536%	$90.8249	$90.82	$90.80	$90.80
Purchase #2	$154.82	12.641%	$174.3908	$174.39	$174.40	$174.40
Purchase #3	$109.79	12.244%	$123.2327	$123.23	$123.25	$123.20
Purchase #4	$86.74	8.589%	$94.1901	$94.19	$94.20	$94.20
Purchase #5	$191.73	13.807%	$218.2022	$218.20	$218.20	$218.20
Purchase #6	$168.60	12.802%	$190.1842	$190.18	$190.20	$190.20
Purchase #7	$145.77	4.556%	$152.4113	$152.41	$152.40	$152.40
7 purchase totals =	$941.91		$1,043.4362	$1,043.42	$1,043.45	$1,043.40