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	$134.29	3.848%	$139.4575	$139.46	$139.45	$139.50
Purchase #2	$50.43	6.270%	$53.592	$53.59	$53.60	$53.60
Purchase #3	$117.46	12.178%	$131.7643	$131.76	$131.75	$131.80
Purchase #4	$200.94	11.314%	$223.6744	$223.67	$223.65	$223.70
Purchase #5	$106.48	7.226%	$114.1742	$114.17	$114.15	$114.20
Purchase #6	$170.69	5.655%	$180.3425	$180.34	$180.35	$180.30
Purchase #7	$147.51	6.676%	$157.3578	$157.36	$157.35	$157.40
7 purchase totals =	$927.80		$1,000.3627	$1,000.35	$1,000.30	$1,000.50