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	$17.25	5.591%	$18.2144	$18.21	$18.20	$18.20
Purchase #2	$113.64	7.873%	$122.5869	$122.59	$122.60	$122.60
Purchase #3	$101.76	7.352%	$109.2414	$109.24	$109.25	$109.20
Purchase #4	$79.90	6.457%	$85.0591	$85.06	$85.05	$85.10
Purchase #5	$181.89	4.457%	$189.9968	$190.00	$190.00	$190.00
Purchase #6	$95.38	5.360%	$100.4924	$100.49	$100.50	$100.50
Purchase #7	$220.43	5.184%	$231.8571	$231.86	$231.85	$231.90
7 purchase totals =	$810.25		$857.4481	$857.45	$857.45	$857.50