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	$42.50	6.352%	$45.1996	$45.20	$45.20	$45.20
Purchase #2	$39.66	3.679%	$41.1191	$41.12	$41.10	$41.10
Purchase #3	$80.67	11.431%	$89.8914	$89.89	$89.90	$89.90
Purchase #4	$197.65	8.440%	$214.3317	$214.33	$214.35	$214.30
Purchase #5	$24.55	13.870%	$27.9551	$27.96	$27.95	$28.00
Purchase #6	$155.69	7.512%	$167.3854	$167.39	$167.40	$167.40
Purchase #7	$184.80	7.596%	$198.8374	$198.84	$198.85	$198.80
7 purchase totals =	$725.52		$784.7197	$784.73	$784.75	$784.70