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	$93.40	6.218%	$99.2076	$99.21	$99.20	$99.20
Purchase #2	$157.61	6.270%	$167.4921	$167.49	$167.50	$167.50
Purchase #3	$206.98	6.312%	$220.0446	$220.04	$220.05	$220.00
Purchase #4	$208.77	6.421%	$222.1751	$222.18	$222.20	$222.20
Purchase #5	$80.72	9.556%	$88.4336	$88.43	$88.45	$88.40
Purchase #6	$169.32	4.483%	$176.9106	$176.91	$176.90	$176.90
Purchase #7	$39.50	4.553%	$41.2984	$41.30	$41.30	$41.30
7 purchase totals =	$956.30		$1,015.5620	$1,015.56	$1,015.60	$1,015.50