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	$113.59	13.326%	$128.727	$128.73	$128.75	$128.70
Purchase #2	$124.92	9.295%	$136.5313	$136.53	$136.55	$136.50
Purchase #3	$196.52	9.102%	$214.4073	$214.41	$214.40	$214.40
Purchase #4	$96.94	12.689%	$109.2407	$109.24	$109.25	$109.20
Purchase #5	$200.47	4.199%	$208.8877	$208.89	$208.90	$208.90
Purchase #6	$44.67	13.865%	$50.8635	$50.86	$50.85	$50.90
Purchase #7	$209.77	3.228%	$216.5414	$216.54	$216.55	$216.50
7 purchase totals =	$986.88		$1,065.1989	$1,065.20	$1,065.25	$1,065.10