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	$231.34	11.554%	$258.069	$258.07	$258.05	$258.10
Purchase #2	$93.34	10.599%	$103.2331	$103.23	$103.25	$103.20
Purchase #3	$216.72	12.144%	$243.0385	$243.04	$243.05	$243.00
Purchase #4	$122.72	7.532%	$131.9633	$131.96	$131.95	$132.00
Purchase #5	$32.37	12.539%	$36.4289	$36.43	$36.45	$36.40
Purchase #6	$85.53	7.207%	$91.6941	$91.69	$91.70	$91.70
Purchase #7	$83.32	3.365%	$86.1237	$86.12	$86.10	$86.10
7 purchase totals =	$865.34		$950.5506	$950.54	$950.55	$950.50