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	$133.88	5.690%	$141.4978	$141.50	$141.50	$141.50
Purchase #2	$219.67	4.800%	$230.2142	$230.21	$230.20	$230.20
Purchase #3	$78.63	8.171%	$85.0549	$85.05	$85.05	$85.10
Purchase #4	$130.54	9.171%	$142.5118	$142.51	$142.50	$142.50
Purchase #5	$156.58	9.133%	$170.8805	$170.88	$170.90	$170.90
Purchase #6	$72.76	12.437%	$81.8092	$81.81	$81.80	$81.80
Purchase #7	$221.84	3.622%	$229.875	$229.88	$229.90	$229.90
7 purchase totals =	$1,013.90		$1,081.8434	$1,081.84	$1,081.85	$1,081.90