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	$45.62	11.646%	$50.9329	$50.93	$50.95	$50.90
Purchase #2	$173.40	13.576%	$196.9408	$196.94	$196.95	$196.90
Purchase #3	$175.47	7.387%	$188.432	$188.43	$188.45	$188.40
Purchase #4	$152.67	12.601%	$171.9079	$171.91	$171.90	$171.90
Purchase #5	$35.82	8.107%	$38.7239	$38.72	$38.70	$38.70
Purchase #6	$164.76	8.766%	$179.2029	$179.20	$179.20	$179.20
Purchase #7	$53.31	7.303%	$57.2032	$57.20	$57.20	$57.20
7 purchase totals =	$801.05		$883.3436	$883.33	$883.35	$883.20