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	$137.67	3.518%	$142.5132	$142.51	$142.50	$142.50
Purchase #2	$117.59	13.526%	$133.4952	$133.50	$133.50	$133.50
Purchase #3	$55.55	6.672%	$59.2563	$59.26	$59.25	$59.30
Purchase #4	$179.40	5.161%	$188.6588	$188.66	$188.65	$188.70
Purchase #5	$179.54	12.755%	$202.4403	$202.44	$202.45	$202.40
Purchase #6	$101.83	12.729%	$114.7919	$114.79	$114.80	$114.80
Purchase #7	$79.50	12.428%	$89.3803	$89.38	$89.40	$89.40
7 purchase totals =	$851.08		$930.5360	$930.54	$930.55	$930.60