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	$244.86	12.271%	$274.9068	$274.91	$274.90	$274.90
Purchase #2	$131.62	3.614%	$136.3767	$136.38	$136.40	$136.40
Purchase #3	$103.44	13.274%	$117.1706	$117.17	$117.15	$117.20
Purchase #4	$26.98	3.116%	$27.8207	$27.82	$27.80	$27.80
Purchase #5	$18.46	10.649%	$20.4258	$20.43	$20.45	$20.40
Purchase #6	$114.92	3.724%	$119.1996	$119.20	$119.20	$119.20
Purchase #7	$53.52	11.767%	$59.8177	$59.82	$59.80	$59.80
7 purchase totals =	$693.80		$755.7179	$755.73	$755.70	$755.70