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	$169.71	6.503%	$180.7462	$180.75	$180.75	$180.70
Purchase #2	$141.69	3.866%	$147.1677	$147.17	$147.15	$147.20
Purchase #3	$158.60	12.785%	$178.877	$178.88	$178.90	$178.90
Purchase #4	$46.68	11.314%	$51.9614	$51.96	$51.95	$52.00
Purchase #5	$119.73	11.351%	$133.3206	$133.32	$133.30	$133.30
Purchase #6	$240.77	11.195%	$267.7242	$267.72	$267.70	$267.70
Purchase #7	$40.54	11.760%	$45.3075	$45.31	$45.30	$45.30
7 purchase totals =	$917.72		$1,005.1046	$1,005.11	$1,005.05	$1,005.10