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	$79.85	7.577%	$85.9002	$85.90	$85.90	$85.90
Purchase #2	$49.75	5.653%	$52.5624	$52.56	$52.55	$52.60
Purchase #3	$168.54	4.760%	$176.5625	$176.56	$176.55	$176.60
Purchase #4	$243.89	12.707%	$274.8811	$274.88	$274.90	$274.90
Purchase #5	$107.67	7.179%	$115.3996	$115.40	$115.40	$115.40
Purchase #6	$147.36	8.512%	$159.9033	$159.90	$159.90	$159.90
Purchase #7	$49.53	11.165%	$55.06	$55.06	$55.05	$55.10
7 purchase totals =	$846.59		$920.2691	$920.26	$920.25	$920.40