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	$5.46	11.736%	$6.1008	$6.10	$6.10	$6.10
Purchase #2	$73.46	12.527%	$82.6623	$82.66	$82.65	$82.70
Purchase #3	$88.55	13.399%	$100.4148	$100.41	$100.40	$100.40
Purchase #4	$55.55	11.439%	$61.9044	$61.90	$61.90	$61.90
Purchase #5	$239.36	11.111%	$265.9553	$265.96	$265.95	$266.00
Purchase #6	$125.57	5.669%	$132.6886	$132.69	$132.70	$132.70
Purchase #7	$38.97	11.718%	$43.5365	$43.54	$43.55	$43.50
7 purchase totals =	$626.92		$693.2627	$693.26	$693.25	$693.30