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	$42.88	4.313%	$44.7294	$44.73	$44.75	$44.70
Purchase #2	$201.42	13.404%	$228.4183	$228.42	$228.40	$228.40
Purchase #3	$236.59	11.756%	$264.4035	$264.40	$264.40	$264.40
Purchase #4	$145.34	10.109%	$160.0324	$160.03	$160.05	$160.00
Purchase #5	$81.86	5.517%	$86.3762	$86.38	$86.40	$86.40
Purchase #6	$81.69	6.223%	$86.7736	$86.77	$86.75	$86.80
Purchase #7	$45.81	10.359%	$50.5555	$50.56	$50.55	$50.60
7 purchase totals =	$835.59		$921.2889	$921.29	$921.30	$921.30