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	$155.54	5.567%	$164.1989	$164.20	$164.20	$164.20
Purchase #2	$192.28	13.567%	$218.3666	$218.37	$218.35	$218.40
Purchase #3	$78.53	11.442%	$87.5154	$87.52	$87.50	$87.50
Purchase #4	$81.63	7.241%	$87.5408	$87.54	$87.55	$87.50
Purchase #5	$17.46	11.787%	$19.518	$19.52	$19.50	$19.50
Purchase #6	$229.28	7.165%	$245.7079	$245.71	$245.70	$245.70
Purchase #7	$147.59	5.730%	$156.0469	$156.05	$156.05	$156.00
7 purchase totals =	$902.31		$978.8945	$978.91	$978.85	$978.80