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	$231.82	4.706%	$242.7294	$242.73	$242.75	$242.70
Purchase #2	$249.65	4.412%	$260.6646	$260.66	$260.65	$260.70
Purchase #3	$128.84	6.432%	$137.127	$137.13	$137.15	$137.10
Purchase #4	$76.93	5.802%	$81.3935	$81.39	$81.40	$81.40
Purchase #5	$80.25	11.183%	$89.2244	$89.22	$89.20	$89.20
Purchase #6	$42.67	6.470%	$45.4307	$45.43	$45.45	$45.40
Purchase #7	$79.47	7.650%	$85.5495	$85.55	$85.55	$85.50
7 purchase totals =	$889.63		$942.1191	$942.11	$942.15	$942.00