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	$80.84	3.661%	$83.7996	$83.80	$83.80	$83.80
Purchase #2	$90.95	9.760%	$99.8267	$99.83	$99.85	$99.80
Purchase #3	$175.26	11.394%	$195.2291	$195.23	$195.25	$195.20
Purchase #4	$142.58	6.547%	$151.9147	$151.91	$151.90	$151.90
Purchase #5	$131.69	11.662%	$147.0477	$147.05	$147.05	$147.00
Purchase #6	$87.46	12.630%	$98.5062	$98.51	$98.50	$98.50
Purchase #7	$129.43	12.768%	$145.9556	$145.96	$145.95	$146.00
7 purchase totals =	$838.21		$922.2796	$922.29	$922.30	$922.20