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	$147.90	11.405%	$164.768	$164.77	$164.75	$164.80
Purchase #2	$31.75	4.497%	$33.1778	$33.18	$33.20	$33.20
Purchase #3	$64.64	8.303%	$70.0071	$70.01	$70.00	$70.00
Purchase #4	$80.64	10.525%	$89.1274	$89.13	$89.15	$89.10
Purchase #5	$182.31	5.209%	$191.8065	$191.81	$191.80	$191.80
Purchase #6	$42.99	9.571%	$47.1046	$47.10	$47.10	$47.10
Purchase #7	$246.56	9.717%	$270.5182	$270.52	$270.50	$270.50
7 purchase totals =	$796.79		$866.5096	$866.52	$866.50	$866.50