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	$159.82	12.610%	$179.9733	$179.97	$179.95	$180.00
Purchase #2	$242.46	11.220%	$269.664	$269.66	$269.65	$269.70
Purchase #3	$61.39	9.553%	$67.2546	$67.25	$67.25	$67.30
Purchase #4	$83.85	6.792%	$89.5451	$89.55	$89.55	$89.50
Purchase #5	$185.27	5.775%	$195.9693	$195.97	$195.95	$196.00
Purchase #6	$20.47	7.597%	$22.0251	$22.03	$22.05	$22.00
Purchase #7	$78.74	5.368%	$82.9668	$82.97	$82.95	$83.00
7 purchase totals =	$832.00		$907.3982	$907.40	$907.35	$907.50