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	$80.37	12.298%	$90.2539	$90.25	$90.25	$90.30
Purchase #2	$128.28	9.690%	$140.7103	$140.71	$140.70	$140.70
Purchase #3	$137.50	13.601%	$156.2014	$156.20	$156.20	$156.20
Purchase #4	$240.40	13.612%	$273.1232	$273.12	$273.10	$273.10
Purchase #5	$147.69	11.377%	$164.4927	$164.49	$164.50	$164.50
Purchase #6	$59.30	13.309%	$67.1922	$67.19	$67.20	$67.20
Purchase #7	$90.34	6.569%	$96.2744	$96.27	$96.25	$96.30
7 purchase totals =	$883.88		$988.2481	$988.23	$988.20	$988.30