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	$78.89	6.307%	$83.8656	$83.87	$83.85	$83.90
Purchase #2	$22.72	5.220%	$23.906	$23.91	$23.90	$23.90
Purchase #3	$39.74	7.130%	$42.5735	$42.57	$42.55	$42.60
Purchase #4	$131.54	6.467%	$140.0467	$140.05	$140.05	$140.00
Purchase #5	$75.77	12.290%	$85.0821	$85.08	$85.10	$85.10
Purchase #6	$26.34	8.541%	$28.5897	$28.59	$28.60	$28.60
Purchase #7	$167.78	7.505%	$180.3719	$180.37	$180.35	$180.40
7 purchase totals =	$542.78		$584.4355	$584.44	$584.40	$584.50