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	$84.47	11.854%	$94.4831	$94.48	$94.50	$94.50
Purchase #2	$38.79	3.272%	$40.0592	$40.06	$40.05	$40.10
Purchase #3	$217.49	3.428%	$224.9456	$224.95	$224.95	$224.90
Purchase #4	$58.53	11.387%	$65.1948	$65.19	$65.20	$65.20
Purchase #5	$248.97	11.786%	$278.3136	$278.31	$278.30	$278.30
Purchase #6	$105.50	4.696%	$110.4543	$110.45	$110.45	$110.50
Purchase #7	$181.73	4.480%	$189.8715	$189.87	$189.85	$189.90
7 purchase totals =	$935.48		$1,003.3221	$1,003.31	$1,003.30	$1,003.40